As filed with the Securities and Exchange Commission on September 30, 1998
                                                 Registration No.

================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                    FORM S-8

             REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933

                          IMCLONE SYSTEMS INCORPORATED
             (Exact name of registrant as specified in its charter)

            Delaware                                          04-2834797
   (State or other jurisdiction of                        (I.R.S. Employer      
    incorporation or organization)                        Identification No.)
                                                    
                                180 Varick Street
                            New York, New York 10014
               (Address of Principal Executive Offices) (Zip code)

    ImClone Systems Incorporated 1996 Incentive Stock Option Plan, As Amended
  ImClone Systems Incorporated 1996 Non-Qualified Stock Option Plan, As Amended
                            (Full title of the plan)

                                   ----------

                                 John B. Landes
            Vice President, Business Development and General Counsel
                          ImClone Systems Incorporated
                                180 Varick Street
                            New York, New York 10014
                     (Name and address of agent for service)

                                 (212) 645-1405
          (Telephone number, including area code, of agent for service)

                                    Copy to:
                           Lawrence A. Darby III, Esq.
                   Kaye, Scholer, Fierman, Hays & Handler, LLP
                                 425 Park Avenue
                          New York, New York 10022-3598

                         CALCULATION OF REGISTRATION FEE

================================================================================
Title of       Amount          Proposed maximum   Proposed maximum  Amount of 
securities to  to be           offering           aggregate         registration
be registered  registered(1)   price per share(2) offering price(2) fee
--------------------------------------------------------------------------------
Common Stock, 
$.001 par      
value .......     1,480 shares     $ 9.625          $    14,246        $    5
              1,161,726 shares       9.699           11,267,581         3,324
                336,794 shares       6.130            2,064,548           609
--------------------------------------------------------------------------------
   Totals ... 1,500,000 shares                      $13,346,375        $3,938
================================================================================

----------
(1)  Excludes such additional  indeterminate number of shares as may be issuable
     pursuant to the  anti-dilution  provisions of the Plans (as defined).  This
     total  represents an additional  1,500,000  shares of Common Stock,  in the
     aggregate,  reserved for issuance  pursuant to options granted or which may
     be  granted  under  either  of  the  ImClone  Systems   Incorporated   1996
     Non-Qualified  Stock  Option  Plan,  As  Amended,  or the  ImClone  Systems
     Incorporated  1996 Incentive Stock Option Plan, As Amended  (together,  the
     "Plans").  With  respect  to the Plans,  1,500,000  of the shares of Common
     Stock reserved for issuance  pursuant  thereto were  previously  registered
     pursuant to the Registrant's  Registration  Statement on Form S-8, File No.
     333-10275,  filed with the Securities and Exchange Commission on August 15,
     1996.

(2)  Estimated  solely for the purposes of  calculating  the  registration  fee.
     Pursuant to Rule 457(c) and Rule 457(h) under the  Securities  Act of 1933,
     as amended,  the proposed maximum offering price per share and the proposed
     maximum aggregate  offering price of shares subject to outstanding  options
     have  been  determined  based  on  the  average  exercise  prices  of  such
     outstanding options and shares not subject to outstanding options have been
     determined  based on the  average  of the high and low prices of the Common
     Stock on September 29, 1998, as reported by NASDAQ National Market.


<PAGE>

REOFFER PROSPECTUS

                          IMCLONE SYSTEMS INCORPORATED

                                2,852,874 SHARES
                                 OF COMMON STOCK

      This Reoffer  Prospectus  (this  "Prospectus")  relates to the reoffer and
resale of an aggregate of 2,852,874  shares (the  "Shares") of the Common Stock,
par value $.001 per share (the "Common Stock"), of ImClone Systems  Incorporated
(the "Company" or the  "Registrant").  The Shares may be acquired,  or have been
acquired,  by certain officers and directors of the Company who may be deemed to
be  "affiliates" of the Company (as defined in Rule 405 under the Securities Act
of 1933,  as amended (the  "Securities  Act")),  all as  identified  herein (the
"Selling  Stockholders"),  from  time to time  upon the  exercise  of (A)  stock
options  ("Options")  granted as of the date of this Prospectus and/or which may
in the  future be  granted  to such  Selling  Stockholders  pursuant  to (i) the
ImClone  Systems  Incorporated  1996 Incentive Stock Option Plan and/or (ii) the
ImClone Systems  Incorporated 1996 Non-Qualified  Stock Option Plan and/or (iii)
the ImClone  Systems  Incorporated  1986 Incentive Stock Option Plan and/or (iv)
the  ImClone  Systems   Incorporated  1986   Non-Qualified   Stock  Option  Plan
(collectively,   the  "Plans")  and  (B)  certain  compensatory   warrants  (the
"Warrants")  to acquire  shares of the Common  Stock of the  Company  previously
issued by the Company to certain of its officers and directors.  The Company may
from time to time supplement  and/or amend this  Prospectus to cover  additional
shares of Common Stock that underlie  Options granted pursuant to one or more of
the Plans to "affiliates" of the Company.

      The Selling  Stockholders may, from time to time, offer all or part of the
Shares on the NASDAQ National Market or such national  securities  exchange upon
which  the  Common  Stock  may be  traded  at the  time of any  such  sales,  in
negotiated  transactions  or by a combination of these methods,  at fixed prices
that may be changed,  at market prices at the time of sale, at prices related to
market prices or at negotiated prices. The Selling Stockholders may effect these
transactions by selling the Shares to or through broker-dealers, who may receive
compensation in the form of discounts or commissions from a Selling Stockholder,
or from the purchasers of the Common Stock for whom the  broker-dealers  may act
as agent or to whom they may sell as  principal,  or from both.  The Company has
paid  or  will  pay  all  expenses  in  connection   with  the  preparation  and
reproduction of the Registration  Statements of which this Prospectus is a part,
which current  expenses are  estimated,  in the aggregate,  to be  approximately
$20,000.  The Company  will not receive any part of the proceeds of any sales by
Selling  Stockholders  of Shares.  However,  the  Company  has  received or will
receive the  exercise  price  payable or paid by Selling  Stockholders  upon the
exercise of Options  issued  under the Plans and upon the  exercise of Warrants.
The Selling  Stockholders will pay the brokerage  commissions charged to sellers
in connection with any sales of Shares thereby hereunder.  In lieu of being sold
pursuant  to this  Prospectus,  any of the Shares  which are  eligible  for sale
pursuant  to Rule 144  under  the  Securities  Act  ("Rule  144") may be sold by
Selling Stockholders under Rule 144. See "Plan of Distribution."

      The Company's  Common Stock trades on the NASDAQ National Market under the
ticker  symbol  "IMCL".  On September  29,  1998,  the closing sale price of the
Common Stock on the NASDAQ National Market was $9 1/16 per share.

      See "RISK FACTORS" beginning on page 7 for a discussion of certain factors
that should be considered  in connection  with an investment in the Common Stock
offered hereby.

      THESE  SECURITIES  HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES
AND  EXCHANGE  COMMISSION  OR ANY  STATE  SECURITIES  COMMISSION,  NOR  HAS  THE
SECURITIES AND EXCHANGE  COMMISSION OR ANY STATE  SECURITIES  COMMISSION  PASSED
UPON THE  ACCURACY OF ADEQUACY OF THIS  PROSPECTUS.  ANY  REPRESENTATION  TO THE
CONTRARY IS A CRIMINAL OFFENSE.

      No dealer,  salesman or any other person has been  authorized  to give any
information or to make any  representations,  other than as contained herein, in
connection  with the  offer  made in this  Prospectus,  and any  information  or
representations  not  contained  herein  must not be relied  upon as having been
authorized by the Company or the Selling Stockholders.  This Prospectus does not
constitute  an offer to sell or a  solicitation  of an offer to buy any security
other than the Common Stock offered by this  Prospectus,  nor does it constitute
an offer to sell or a solicitation of an offer to buy any shares of Common Stock
offered  hereby to any person in any  jurisdiction  where it is unlawful to make
such an offer or  solicitation  to such  person.  Neither  the  delivery of this
Prospectus  nor any sale  hereunder  shall  under any  circumstances  create any
implication  that  information  contained  herein  is  correct  as of  any  time
subsequent to the date hereof.

               The date of this Prospectus is September 30, 1998.

<PAGE>

                        SECTION 10(a) PROSPECTUS; REOFFER
                     PROSPECTUS; POST-EFFECTIVE AMENDMENT TO
                    PREVIOUSLY FILED REGISTRATION STATEMENTS

      Section  10(a)  Prospectus.   The  documents  containing  the  information
specified in Part I of this  Registration  Statement on Form S-8 will be sent or
given to  participants  in the Plans as  specified by Rule  428(b)(i)  under the
Securities  Act of 1933, as amended.  Such documents are not required to be, and
are not being, filed by the Company with the Securities and Exchange Commission,
either as part of this  Registration  Statement or as prospectuses or prospectus
supplements  pursuant to Rule 424 under the  Securities Act of 1933, as amended.
Such documents,  together with the documents  incorporated  by reference  herein
pursuant  to  Item 3 of  Part II of this  Registration  Statement  on Form  S-8,
constitute  a prospectus  that meets the  requirements  of Section  10(a) of the
Securities Act of 1933, as amended.

      Reoffer Prospectus. The material which follows up to but not including the
page beginning Part II of this  Registration  Statement,  constitutes a "reoffer
prospectus," prepared in accordance with the requirements of Part I of Form S-3,
in accordance  with General  Instruction C of Form S-8, to be used in connection
with  reoffers  and resales of  securities  acquired  under the ImClone  Systems
Incorporated  1996 Incentive  Stock Option Plan, As Amended,  and/or the ImClone
Systems Incorporated 1996 Non-Qualified Stock Option Plan, As Amended and/or the
ImClone Systems  Incorporated  1986  Non-Qualified  Stock Option Plan and/or the
ImClone Systems 1986 Incentive  Stock Option Plan and/or under certain  warrants
to acquire shares of Common Stock of the Registrant.

      Post-Effective  Amendment to  Previously  Filed  Registration  Statements.
Pursuant to Rule 429 under the Securities Act of 1933, as amended,  the "reoffer
prospectus"  included as part of this  Registration  Statement  on Form S-8 also
relates to certain  securities  registered under ImClone Systems  Incorporated's
Registration Statement on Form S-8 (File No. 33-95894) filed with the Securities
and Exchange  Commission  and declared  effective on August 24, 1995 and ImClone
Systems  Incorporated's  Registration Statement on Form S-8 (File No. 333-10275)
filed with the  Securities  and Exchange  Commission  and declared  effective on
August 15, 1996 (together, the "Prior Registration Statements"), is intended for
use therewith and  constitutes a  post-effective  amendment to each of the Prior
Registration  Statements.   Such  "reoffer  prospectus"  is  being  filed  as  a
post-effective  amendment  to  each  of the  Prior  Registration  Statements  in
reliance  upon  Item  3(a) of  General  Instruction  C of  Form  S-8  under  the
Securities Act of 1933, as amended.


                                       -i-

<PAGE>

                                TABLE OF CONTENTS

                                                                           Page

AVAILABLE INFORMATION.......................................................1
INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE.............................1
CERTAIN FACTORS AFFECTING FORWARD LOOKING STATEMENTS........................2
PROSPECTUS SUMMARY..........................................................2
RISK FACTORS................................................................7
USE OF PROCEEDS............................................................13
SELLING STOCKHOLDERS.......................................................14
PLAN OF DISTRIBUTION.......................................................16
LEGAL MATTERS..............................................................16
DISCLOSURE OF COMMISSION POSITION ON 
INDEMNIFICATION FOR SECURITIES ACT LIABILITIES.............................17


                                      -ii-

<PAGE>

                              AVAILABLE INFORMATION

      The Company has filed three separate  Registration  Statements on Form S-8
(the "Registration Statements") under the Securities Act with the Commission (as
defined),  with  respect to the shares of Common  Stock of the  Company  offered
hereby.  As  permitted  by the rules and  regulations  of the  Commission,  this
Prospectus omits certain  information  contained in the Registration  Statements
and the exhibits and schedules thereto.  For further information with respect to
the Company and the Common Stock offered  hereby,  the Company is subject to the
informational  requirements  of the Securities  Exchange Act of 1934, as amended
(the  "Exchange  Act"),  and  in  accordance  therewith  files  reports,   proxy
statements  and  other  information  with  the  U.S.   Securities  and  Exchange
Commission  (the  "Commission").   Such  reports,  proxy  statements  and  other
information filed by the Company with the Commission can be inspected and copied
at the Public  Reference Room  maintained by the Commission at 450 Fifth Street,
N.W., Room 1024,  Washington,  D.C.,  20549,  and at the regional offices of the
Commission at 7 World Trade Center,  13th Floor,  New York, New York,  10048 and
Northwestern  Atrium  Center,  500 West  Madison  Street,  Room  1400,  Chicago,
Illinois  60661-2511.  Copies of such  material can be obtained  from the Public
Reference Room of the Commission at 450 Fifth Street, N.W., Washington, D.C., at
prescribed  rates.  Information  regarding the operation of the Public Reference
Room may be obtained by calling the Commission at 1-800-SEC-0330. The Commission
maintains a World Wide Web site that  contains  reports,  proxy and  information
statements and other information  regarding registrants that file electronically
with  the  Commission.  The  address  of that  site is  http://www.sec.gov.  The
Company's  Common Stock is traded on the NASDAQ National Market under the ticker
symbol  "IMCL."  Reports,  proxy  statements and other  information  may also be
inspected at the NASDAQ National Market offices located at 1735 K Street,  N.W.,
Washington, D.C. 20006.

      Statements contained in this Prospectus as to the contents of any contract
or other document referred to are not necessarily complete, and in each instance
reference  is made to the copy of such  contract or other  document  filed as an
Exhibit to the  applicable  Registration  Statement or otherwise  filed with the
Commission,  each  such  statement  being  qualified  in all  respects  by  such
reference,  and each  such  contract  or other  document  shall be  deemed to be
incorporated by reference into this Prospectus.

                 INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

      The following documents, including all amendments filed for the purpose of
completing  or updating such reports,  which have been  heretofore  filed by the
Company with the Commission pursuant to the Exchange Act are hereby incorporated
by reference and made a part hereof:

      1.    The  Company's  Annual Report on Form 10-K for the fiscal year ended
            December 31, 1997.

      2.    The Company's Quarterly Reports on Form 10-Q for the fiscal quarters
            ended March 31, 1998 and June 30, 1998.

      3.    The Company's  Current  Report on Form 8-K, dated February 10, 1998.
            
      4.    The description of the Company's  Common Stock,  par value $.001 per
            share,contained  in its  registration  statement  on Form 8-A  filed
            under the Exchange Act,  including any amendment or report filed for
            the purpose of updating such description.

      All other documents  filed by the Company with the Commission  pursuant to
Sections  13(a),  13(c), 14 and 15(d) of the Exchange Act subsequent to the date
of this Prospectus and prior to the filing of a post-effective  amendment to the
applicable  Registration  Statement which indicates that all securities  offered
have been sold or which de-registers all securities then remaining unsold, shall
be deemed to be  incorporated  by reference in this  Prospectus and to be a part
hereof  from the date of  filing  of such  documents  (such  documents,  and the
documents  enumerated above,  being hereinafter  referred to collectively as the
"Incorporated Documents").

         Any statement contained in an Incorporated  Document shall be deemed to
be modified or superseded  for purposes of this  Prospectus to the extent that a
statement  contained  therein or in any other  subsequently  filed  Incorporated
Document modifies or supersedes such statement.  Any such statements so modified
or  superseded  shall not be deemed,  except as so  modified or  superseded,  to
constitute a part of this Prospectus.


                                       1

<PAGE>

      The Company undertakes to provide without charge to each person (including
any beneficial owner) to whom a copy of this Prospectus is delivered,  upon oral
or written request of such person, a copy of any and all of the information that
has been or may be  incorporated  by  reference in this  Prospectus,  other than
exhibits to such  documents.  Requests for such copies should be directed to the
attention of John B. Landes,  Vice President,  Business  Development and General
Counsel,  ImClone Systems Incorporated,  180 Varick Street, 7th Floor, New York,
New York 10014; (212) 645-1405.

              CERTAIN FACTORS AFFECTING FORWARD LOOKING STATEMENTS

      This  Prospectus,  including the documents  and  information  incorporated
herein by reference,  contains forward-looking  statements within the meaning of
Section 27A of the  Securities  Act that  involve  risks and  uncertainties.  In
connection with the safe harbor provisions of the Private Securities  Litigation
Reform  Act of 1995,  the  Company  is hereby  providing  cautionary  statements
identifying  important  factors that could cause the Company's actual results to
differ  materially  from those expressed in  forward-looking  statements made in
this Prospectus,  including the documents and information incorporated herein by
reference. Any statements that express beliefs, plans,  objectives,  assumptions
or future events or performance (often, but not always, through the use of words
of phrases such as "will likely result," "are expected to," "will continue," "is
anticipated,"  "estimate,"  "intends," "plans," "projection," and "outlook") may
be  forward-looking  and,  accordingly,  such statements may involve  estimates,
assumptions,  risks and  uncertainties  which  could  cause  actual  results and
performance  of the Company to differ  materially  from those  expressed  in the
forward-looking  statements.  In  evaluating  the  Company  and its  operations,
performance and results,  investors should consider, among other things, and any
forward-looking  statements  contained in this Prospectus are qualified in their
entirety by reference to, the factors  discussed  herein under the caption "Risk
Factors" and the estimates,  assumptions,  risks and uncertainties  discussed in
the  Company's  most  recent  Annual  Report  on Form 10-K  under  the  captions
"Business" and "Management's  Discussion and Analysis of Financial Condition and
Results of Operations," in the Company's  Quarterly Reports on Form 10-Q, and in
the  Company's  other  reports  filed  under  the  Exchange  Act,  in each  case
incorporated by reference herein.

      The risk factors  described  herein could cause actual results or outcomes
to differ materially from those expressed in any  forward-looking  statements of
the Company or made by or on behalf of the Company,  and  investors,  therefore,
should not place undue reliance on any such forward-looking statements. Further,
any forward-looking statement speaks only as of the date on which such statement
is made, and the Company undertakes no obligation to update any  forward-looking
statement or statements  to reflect  events or  circumstances  after the date on
which such  statement  is made or to reflect  the  occurrence  of  unanticipated
events.  New  factors  emerge  from  time to time,  and it is not  possible  for
management  of the Company to predict all of such factors.  Further,  management
cannot  necessarily  assess  the  impact  of each such  factor on the  Company's
business or the extent to which any factor, or combination of factors, may cause
actual results to differ materially from those contained in any  forward-looking
statements.

                               PROSPECTUS SUMMARY

      The  following  summary is qualified in its entirety by the more  detailed
information,  "Risk  Factors"  and  financial  statements,  including  the notes
thereto,  included  or  incorporated  by  reference  in  this  Prospectus.   The
securities offered hereby involve a high degree of risk. See "Risk Factors."

      General.

      The Company is a  biopharmaceutical  company engaged primarily in research
and  development  of  therapeutic  products  for the  treatment  of  cancer  and
cancer-related    disorders.    The   Company's   product   candidates   include
interventional therapeutics for cancer and cancer vaccines.

      Development Programs.

      C225 Cancer Therapeutic. The Company's lead interventional therapeutic for
cancer is a chimerized (part mouse,  part human) antibody that acts to block the
Epidermal  Growth  Factor  receptor   ("EGFr").   EGFr  has  been  shown  to  be
over-expressed in the cells of approximately  one-third of all solid cancers. It
is also  expressed in select normal  tissue.  In vivo animal  studies with human
tumors have shown that C225 in combination with various  chemotherapeutic agents
(doxorubicin,  cisplatin or paclitaxel) demonstrates a pronounced enhancement of
the  anti-tumor  effect  of  the  chemotherapeutic   agents,  resulting  in  the
elimination  of human  tumors  established  in these  animals.  The studies have
demonstrated  long-term  tumor-free survival 

 
                                      2
<PAGE>

of  animals.  The  Company's  research  has also  shown that C225 used alone has
efficacy in renal cell carcinoma and pancreatic carcinoma animal models.

      Since  December  1994,  the Company has  initiated  several  Phase  Ib/IIa
clinical  trials of C225 at Memorial  Hospital (the patient care arm of Memorial
Sloan-Kettering   Cancer  Center)   ("Sloan-Kettering"),   Yale  Cancer  Center,
University of Virginia, MD Anderson Cancer Center and the University of Alabama,
among  others.  These  studies  have  involved  intravenous   administration  of
escalating  doses of C225,  both with and without  chemotherapeutic  agents,  in
patients with various solid cancers. Several of these studies are ongoing. These
studies  have  shown that the drug is  generally  well-tolerated.  In 1997,  the
Company  initiated  Phase Ib/IIa studies in head and neck cancer  patients using
C225 alone (begun in July 1997), in conjunction  with cisplatin  (begun in April
1997) and in conjunction with radiation (begun in April 1997). Additionally,  in
December  1997,  the  Company  initiated  a  multi-center,  open label  Phase II
clinical  trial to evaluate the effect of C225 on time to progression of disease
in 53 patients with  metastatic  renal cell  carcinoma.  The Company  expects to
initiate  Phase  II/III  studies to evaluate  the  potential  of C225 in various
additional tumor types, such as head and neck and pancreatic cancers.

      BEC2 Cancer Vaccine.  BEC2 is a monoclonal  anti-idiotypic  antibody which
the Company  believes  may be useful to prevent or delay the onset of  recurrent
primary tumors or metastatic disease. The antibody, which mimics the ganglioside
GD3,  has been tested since 1991 in Phase I clinical  trials at  Sloan-Kettering
against  certain  forms of  cancer,  including  small  cell lung  carcinoma  and
melanoma.  There has been evidence of prolonged  survival of patients with small
cell lung  carcinoma in a pilot study  involving  BEC2 at  Sloan-Kettering.  The
Company has granted  Merck KGaA,  formerly E. Merck  ("Merck"),  a  German-based
pharmaceutical  company,   exclusive  rights  to  manufacture  and  market  BEC2
worldwide,  except  that in North  America,  Merck  does  not have the  right to
manufacture  BEC2 and the Company has retained the right to co-promote  BEC2. It
is the  intent  of the  parties  that  the  Company  will  be the  bulk  product
manufacturer of BEC2 to support worldwide sales. In return,  Merck is paying the
Company  research  support,  is required to pay the Company  milestone  fees and
royalties  on future  sales,  if any,  and will share with the Company  revenues
associated  with  the  sale of BEC2 by  Merck  in  North  America.  A Phase  III
multinational clinical trial for BEC2 in treatment of limited disease small cell
lung carcinoma has been opened and patient enrollment has been initiated.

      Chimerized Monoclonal Antibody Inhibitor of Angiogenesis.  The Company has
developed a monoclonal antibody, c-p1C11, which is specific for the KDR receptor
for Vascular  Endothelial  Growth Factor ("VEGF").  The antibody is currently in
pre-clinical  studies in preparation  for the filing of an  Investigational  New
Drug ("IND")  Application  and the further testing of the product as a potential
cancer  therapeutic.  The  Company is also  preparing  a  humanized  form of the
antibody,  in conjunction with MRC Collaborative  Center. KDR and VEGF are known
to be involved in  angiogenesis,  which is the natural  process of growth of new
blood vessels. A therapeutic product that would inhibit angiogenesis could be of
value in treatment of cancer as well as other  diseases that depend on growth of
blood vessels, such as diabetic retinopathy, macular degeneration and rheumatoid
arthritis.

      Research Programs.

      In addition to concentrating on its products in clinical development,  the
Company performs ongoing research in a number of related areas.

      Interventional Therapeutics. The Company conducts an interventional cancer
therapeutic research program in the development of inhibitors of tyrosine kinase
receptors (growth factor receptors)  associated with tumor cell regeneration and
support.

      In addition to its  chimerized  monoclonal  antibody in  development,  the
Company is seeking to develop other  antibodies  that inhibit  angiogenesis.  In
connection  with this research and  development of the  chimerized  angiogenesis
inhibitor,  the Company is  sponsoring  research  programs  at various  academic
institutions to test KDR specific therapeutics in animal models.

      The  Company  has also  initiated  a program  to  develop  small  molecule
antagonists of growth factor receptors,  including both angiogenic growth factor
receptors  and EGF  receptors.  In October  1997,  the Company  entered  into an
agreement with CombiChem, Inc. ("CombiChem"), a combinational chemistry company,
pursuant  to which the  Company  has  access  to  CombiChem's  library  of small
molecules  for  screening in the  Company's  assays for  identification  of lead
candidates. The Company also made an equity investment in CombiChem. The Company
has also entered into an agreement with the Institute for Molecular  Medicine in
Freiburg,  Germany to screen small molecule  therapeutic  candidates,  including
those provided by the compound libraries of CombiChem,  against various tyrosine
receptors.


                                       3
<PAGE>

      The Company is conducting research on the validation of  vascular-specific
cadherin   ("VE-cadherin")   as  a  novel   potential  drug  target  to  inhibit
cancer-associated  angiogenesis.  VE-cadherin  is believed to play an  important
role in angiogenesis by enabling the assembly of endothelial cells into vascular
tubes.  Cancer growth is dependent on the formation of a capillary  blood vessel
network in the  tumor,  and  VE-cadherin  antagonists  may thus have  utility as
anti-cancer  agents.  The  Company  will  test  monoclonal   antibodies  against
VE-cadherin as potential  angiogenesis  inhibitors  and use its  high-throughput
assays for the  identification  of small  molecule  VE-cadherin  inhibitors.  In
connection with this program,  the Company has also acquired exclusive rights to
VE-cadherin-2   and  to   antibodies  to   VE-cadherin,   and  has  initiated  a
collaboration  with Mario Negri Institute for  Pharmacological  Research (Milan,
Italy)  to  conduct  pharmacological  research  in the role of  VE-cadherins  in
antiogenesis.

      Cancer Vaccines.  The Company seeks to discover  potential cancer vaccines
as another route to cancer  treatment.  Cancer  vaccines would  activate  immune
responses to tumors to protect  against  local  spread,  distant  metasteses  or
recurrence of cancer.  Choosing  appropriate  cancer cell targets and generating
effective  immune  responses  are the  focus  of the  Company's  cancer  vaccine
program.  For  example,  research  is being  conducted  on a possible  malignant
melanoma vaccine based on the tumor associated  antigen known as gp75.  Patients
with  malignant  melanoma  are  known to  produce  antibodies  and T cells  that
recognize  gp75.  Animal studies have shown that a gp75 cancer vaccine is highly
effective in eliciting an immune response  against melanoma cells and preventing
or inhibiting growth of experimental melanoma tumors in mice.

      Endothelial Stem Cell Technology.  The Company has proprietary  technology
capable of isolating endothelial stem cells and is exploring uses of endothelial
stem cells for stimulation of collateral  blood  circulation in ischemias (e.g.,
myocardial ischemia and peripheral vascular disease) as well as for gene therapy
delivery. The Company is considering whether to pursue this research directly or
through   its   recently   established   wholly-owned   subsidiary,    EndoClone
Incorporated.

      Hematopoiesis. The Company is conducting research in hematopoiesis (growth
and development of blood cell elements) aimed at discovering  factors to support
hematopoietic stem cells and to control the proliferation,  differentiation  and
functional deterioration of hematopoietic elements.

      The Company has an  exclusive  license  from The  National  Institutes  of
Health ("NIH") to the delta-like  ("DLK")  protein and gene for use in stem cell
and gene therapy.  DLK is a member of a family of proteins  which appear to have
the ability to maintain cells in an undifferentiated state.

      The  Company  also has  entered  into a  non-exclusive  license and supply
agreement with Immunex Corporation ("Immunex") for use of the FLK-2/FLT-3 ligand
for ex vivo cell therapies.  Immunex has taken a license from the Company to the
FLK-2  receptor,  the scope of which is  limited  to the use by  Immunex  in the
manufacture of the FLK-2/FLT-3  ligand.  Immunex is currently testing the ligand
in human trials for stem cell mobilization and for tumor inhibition.

      The Company also has rights to  recombinant  mutein form of  Interleukin-6
("interleukin-6m"  or  "IL-6m")  which it has  tested in human  trials in cancer
patients to seek to  stimulate  platelet  production.  The Company is  currently
monitoring third party research with IL-6m to explore the possibility that IL-6m
may be a critical factor in liver cell regeneration.

      Licensed Diagnostics and Infectious Disease Vaccines.

      The Company has licensed its  diagnostic and  infectious  disease  vaccine
product areas, based on its earlier research,  to corporate partners for further
development  and  commercialization.  The Company has granted the  Wyeth/Lederle
vaccine and pediatrics division of American Home Products Corporation ("American
Home") a worldwide  license to  manufacture  and market its  infectious  disease
vaccines, which are in development. In January 1998, this agreement was extended
to allow the  continuation  through  September 1999 of pre-clinical  research in
preparation for clinical trials of infectious disease candidate vaccines for the
treatment  of  gonorrhea  and the receipt by the Company of annual  funding from
American Home during such period in the amount of $300,000. The Company has also
entered into a strategic alliance with Abbott  Laboratories  ("Abbott") pursuant
to which the Company has licensed  certain of its diagnostic  products to Abbott
on a worldwide basis. In mid-1995, Abbott launched in Europe its first DNA-based
test,  using the Company's  proprietary  Repair Chain Reaction ("RCR") DNA probe
technology,  for the diagnosis of the sexually  transmitted  disease  chlamydia.
Abbott has added tests for gonorrhea and mycobacteria, and has launched sales in
the United States as well.  In December  1996,  the Company and Abbott  modified
this  agreement to provide for an exclusive  sublicensing  agreement with Chiron
Diagnostics  ("Chiron")  for the  Company's  patented  DNA signal  amplification
technology,  AMPLIPROBE.  Under the terms of the  agreement  all sales of Chiron
branched DNA diagnostic probe technology in countries covered by Company patents
will be subject to a royalty to Abbott to be passed through to the Company.


                                       4
<PAGE>

      Research and Development.

      The Company  initiated its in-house  research and development in 1986. The
Company has assembled a scientific staff with a variety of complementary  skills
in  a  broad  base  of  advanced  research  technologies,   including  oncology,
immunology,  molecular  and cell  biology,  antibody  engineering,  protein  and
synthetic  chemistry  and  high-throughput   screening.  The  Company  has  also
recruited  a  staff  of  technical  and  professional  employees  to  carry  out
manufacturing  of  clinical  trial  materials  at  its  Somerville,  New  Jersey
manufacturing  facility.  In addition to its research programs pursued in-house,
the Company collaborates with certain academic  institutions and corporations to
support  research in areas of the Company's  product  development  efforts.  The
Company has also entered into collaborations with major pharmaceutical companies
in order  to  obtain  funding  and  product  development  and  commercialization
assistance  for certain of its  therapeutic  product  candidates in exchange for
specific product licensing rights.  The Company intends to enter into additional
agreements of this nature with appropriate  pharmaceutical company partners with
the resources and experience to assist the Company  financially to  successfully
bring its products to market, both in the United States and abroad. There can be
no assurance,  however,  that the Company will be successful in consummating any
such arrangements.

      In addition to its research programs pursued in-house and in collaboration
with  corporate  partners,   the  Company  collaborates  with  certain  academic
institutions  to support  research  in areas  related to the  Company's  product
development  efforts.  These institutions  include,  but are not limited to, the
National  Cancer  Institute,  Sloan-Kettering,  the  University  of  California,
Princeton  University,  the University of North Carolina,  The Wistar Institute,
The  University  of  Texas  Southwestern  Medical  Center  and The  Mario  Negri
Institute for Pharmacological  Research.  Usually, research supported at outside
academic  institutions  is performed in  conjunction  with  additional  in-house
research.  The Company also has collaborations with institutions  related to the
performance  of its clinical  trials.  Such  institutions  include,  but are not
limited to, Sloan-Kettering,  Yale Cancer Center, the University of Virginia, MD
Anderson Cancer Center, and the University of Alabama.

      The  Company  operates  a  facility  in  Somerville,  New  Jersey  for the
manufacture  of bulk  materials  of its  therapeutic  candidates  in quality and
quantity sufficient for human clinical trials. At this facility,  the Company is
producing C225 bulk drug. At this facility,  the Company also supports  clinical
development of both the C225 and BEC2 programs.

      The  Company  was  incorporated  in  Delaware  in 1984 and  commenced  its
principal  research and  development  operations  in March 1986.  The  Company's
principal  executive  offices and laboratories are located at 180 Varick Street,
New York, New York, 10014, and the telephone number is (212) 645-1405.

      The Offering.

Common Stock being Offered ............      The   Prospectus   relates   to  an
                                             offering     by     the     Selling
                                             Stockholders  of  up  to  2,852,874
                                             shares of Common Stock which may be
                                             acquired,  or have been acquired by
                                             such Selling  Stockholders upon the
                                             exercise  of  Options  issued as of
                                             the  date  of  this  Prospectus  or
                                             thereafter under the Plans and upon
                                             the exercise of the Warrants.

Common Stock Outstanding
   after the Offering .................      As  of   September   25,  1998  the
                                             Company  had  24,437,522  shares of
                                             Common Stock outstanding.  Assuming
                                             that   all  of  the   Options   and
                                             Warrants     held    by     Selling
                                             Stockholders as of the date of this
                                             Prospectus  are  exercised  and  no
                                             other  shares of  Common  Stock are
                                             issued  following  the date of this
                                             Prospectus,  the Company would have
                                             26,833,901 shares of  Common  Stock
                                             outstanding.

Use of Proceeds .......................      The  Company  will not  receive any
                                             proceeds   from  the  sale  of  the
                                             Shares   offered  by  the   Selling
                                             Stockholders.  However, the Company
                                             has  received  or will  receive the
                                             exercise  price  payable or paid by
                                             Selling   Stockholders   upon   the
                                             exercise  of Options  issued  under
                                             the Plans and upon the  exercise of
                                             Warrants. If all of the Options and
                                             Warrants   held   by  the   Selling
                                             Stockholders as of the date of this
                                             Prospectus   are   exercised,   the
                                             Company  will   receive   aggregate
                                             estimated  proceeds  in  connection
                                             with the  payment  of the  exercise
                                             prices of such Options and Warrants
                                             (including any amounts 
 

                                       5

<PAGE>

                                             received in respect  thereof by the
                                             Company  in  connection   with  the
                                             exercise  of Options  and  Warrants
                                             prior   to   the   date   of   this
                                             Prospectus)    of     approximately
                                             $17,562,000.       The      Company
                                             anticipates   using  any   proceeds
                                             received,  and has  used  any  such
                                             proceeds previously received,  upon
                                             the  exercise  of the  Options  and
                                             Warrants  (i) to  continue  to fund
                                             and   expand   its   research   and
                                             development  programs  and (ii) for
                                             general     corporate     purposes,
                                             including working capital. See "Use
                                             of Proceeds." 
NASDAQ National
  Market Symbol........................      IMCL

Risk Factors...........................      See "Risk Factors" for a discussion
                                             of certain risk factors that should
                                             be   considered   by    prospective
                                             investors  in  connection  with  an
                                             investment  in the  Shares  offered
                                             hereby.


                                       6

<PAGE>

                                  RISK FACTORS

      An investment  in the Shares  offered by this  Prospectus  involves a high
degree of risk. In addition to the other  information  contained or incorporated
by reference in this  Prospectus,  the  following  factors  should be considered
carefully in evaluating an investment in the Shares offered hereby.

      Early Stage of Product Development; Technological Uncertainty.

      The Company was founded in 1984 and opened its  laboratory  in New York in
1986.  Substantially all of the Company's  products are in research or the early
stages of development or clinical  studies.  Substantially  all of the Company's
revenues were  generated from license and research  arrangements  with corporate
sponsors.  The Company's revenues under its research and license agreements with
corporate  sponsors have fluctuated and are expected to fluctuate  significantly
from period to period.  Similarly,  the  Company's  results of  operations  have
fluctuated  and are expected to fluctuate  significantly  from period to period.
These  variations  have been,  and are  expected to be,  based  primarily on the
timing of entering into supported research and license agreements, the status of
development of the Company's various products,  the timing and level of revenues
from sales by its  partner in  diagnostics,  Abbott,  of  products  bearing  the
Company's  technology,  the  addition or  termination  of  research  programs or
funding support,  performance by the Company's corporate  collaborators of their
funding obligations,  the achievement of specified research or commercialization
milestones  and  variations  in the  level  of  expenditures  for the  Company's
proprietary  products  during any given  period.  The  Company's  products  will
require substantial  additional  development and clinical testing and investment
prior to commercialization. To achieve profitable operations, the Company, alone
or with others, must successfully develop, introduce and market its products. No
assurance can be given that any of the  Company's  product  development  efforts
will be  successfully  completed,  that  required  regulatory  approvals  can be
obtained or that any products, if developed,  will be successfully  manufactured
or marketed or achieve customer acceptance.

      History of Operating Losses and Accumulated Deficit.

      The  Company has  experienced  significant  operating  losses in each year
since its  inception,  due  primarily to  substantial  research and  development
expenditures.  As of June 30, 1998,  the Company had an  accumulated  deficit of
approximately $125 million. The Company expects to incur significant  additional
operating losses over each of the next several years.

      Cash Requirements; Need for Additional Funding.

      The  Company  has  expended  and will  continue  to expend  in the  future
substantial  funds to continue  the research and  development  of its  products,
conduct   preclinical  and  clinical  trials,   establish   clinical-scale   and
commercial-scale  manufacturing  in its own  facilities or in the  facilities of
others, and market its products.

      The Company  expects to incur  substantial  funding  requirements  for the
expansion of operations,  including (i) the expansion of the clinical  trials of
C225 and the related  manufacturing  program to support  these  trials which may
include  expansion of the Company's  facilities and (ii) in an effort to develop
new product  candidates,  the expansion of research and  development  activities
including among other things,  increased staffing, the acquisition of equipment,
and the consummation of new outside research agreements. In addition, $2,200,000
of the Industrial  Development  Revenue Bonds issued by the New York  Industrial
Development  Agency  ("NYIDA") in 1990 with a scheduled  maturity in 2004 become
due upon the earlier  termination  of the lease (the  "Lease") for the Company's
New York facility.  The Lease is scheduled to expire in March 1999, however, the
Company  currently  expects  to be able to extend  the Lease  and  retrofit  the
facility to better suit its needs,  although  there is no assurance that it will
be able to do so. Assuming the extension of the Lease,  the Company expects that
the ongoing research support of its corporate partners,  together with its other
capital  resources,  will be  sufficient  to enable it to fund its  current  and
planned  operations  through the end of the year 2000. The receipt of certain of
such ongoing  research  support is subject to the  attainment  by the Company of
specified  research and  development  milestones,  certain of which have not yet
been  achieved.  No  assurance  can be given  that there will not be a change in
projected research support (including research and development  milestones),  or
in other  expenses that would lead to the Company's  capital being consumed at a
faster rate than  currently  expected,  or that the Lease will be extended.  The
Company will require  significant  levels of  additional  capital and intends to
raise the necessary  capital  through  additional  arrangements  with  corporate
partners, equity or debt financings or from other sources. There is no assurance
that the Company will be successful in  consummating  any such  arrangements  or
financings.  If adequate funds are not available, the Company may be required to
significantly curtail its planned operations.


                                       7

<PAGE>

      The Company has entered into  preliminary  discussions  with several major
pharmaceutical  companies concerning the funding of research and development for
certain of its products in research.  No assurance can be given that the Company
will be successful in pursuing any such alternatives.  In addition,  the Company
is in preliminary  discussions with several major pharmaceutical  companies with
respect  to a  strategic  alliance  for  the  development  of its  lead  product
candidate,  C225.  Such a strategic  alliance  could include an up-front  equity
investment  by such a company  in the  Company,  as well as the  payment  to the
Company of technology access fees, milestone fees and revenue sharing. There can
be no  assurance  that the  Company  will be  successful  in  achieving  such an
alliance,  nor can the  Company  predict  the  amount  of funds  which  might be
available  to it if it entered  into such an  alliance or the time at which such
funds would be made available.

      Pursuant  to the terms of the  Company's  Series A  Convertible  Preferred
Stock (the  "Series A  Preferred  Stock" or "Series A  Preferred  Shares"),  the
holders of the Series A Preferred  Shares are entitled to receive,  out of funds
legally available therefor, cumulative dividends at the annual rate of $6.00 per
share, compounded annually. Dividends are payable on the then outstanding Series
A Preferred  Shares in cash upon the earlier of (i) annually on December 31st of
each year  beginning on December 31, 1999;  or (ii) at the time of conversion or
redemption of the Series A Preferred Shares on which the dividend is being paid.
Dividends on the Series A Preferred  Shares  accumulate and accrue from December
15, 1997 (the date of original issuance) and accrue  thereafter,  whether or not
earned or declared.  As of June 30, 1998,  dividends  aggregating  approximately
$1,302,000 had accrued on the Series A Preferred Shares.

      Dilution.

      Warrants to purchase 2,281,050 shares of the Company's Common Stock (which
includes  1,314,850  warrants  held  by  directors,   officers,   employees  and
consultants of the Company), at an average exercise price of approximately $2.79
per share (subject to adjustment) and stock options to purchase 4,548,424 shares
of the  Company's  Common Stock (which  includes  4,098,424  options  granted to
directors,  officers,  employees  and  consultants  of  the  Company  under  the
Company's stock option plans at an average exercise price of approximately $7.90
per share (subject to  adjustment),  were  outstanding as of September 25, 1998.
The shares  underlying  such  options and  warrants  (including  the Options and
Warrants which are covered by this  Prospectus) are covered,  or will be covered
prior  to  exercise,  by  effective  registration  statements  on file  with the
Commission.  For the life of such options and warrants,  the holders thereof are
given an  opportunity  to benefit  from a rise in the market price of the Common
Stock with a resulting  dilution  of the  interest  of other  stockholders.  The
exercise of such options and warrants is likely to be  undertaken at a time when
the Company, in all probability, could obtain additional equity capital from the
public on terms more  favorable  than those provided for pursuant to the options
and warrants.  The exercise of a  significant  number of options and warrants at
any one time or the sale of a  substantial  number of  shares  of  Common  Stock
acquired upon exercise of options or warrants could adversely  affect the market
price  of the  Company's  Common  Stock  and  the  Company's  ability  to  raise
additional equity capital.

      As  of  September  25,  1998,  400,000  Series  A  Preferred  Shares  were
outstanding.  The Series A Preferred Shares have a stated value of $100. 100,000
Series A Preferred  Shares were  immediately  convertible  into Common  Stock on
December  15,  1997  (the  "Issuance  Date");  an  additional  100,000  Series A
Preferred  Shares  become  convertible  on or after January 1, 2000 (the "Second
Anniversary  Date");  an  additional  100,000  Series A Preferred  Shares become
convertible on or after January 1, 2001 (the "Third  Anniversary  Date"); and an
additional  100,000  Series A Preferred  Shares become  convertible  on or after
January 1, 2002 (the  "Fourth  Anniversary  Date").  Series A  Preferred  Shares
converted on or after the Issuance  Date and before the Second  Anniversary  are
convertible at a per share conversion price of $12.50; Series A Preferred Shares
converted  on or  after  the  Second  Anniversary  Date  and  before  the  Third
Anniversary  Date are convertible at a per share  conversion  price equal to the
Average  Market Price of the Common Stock for the five (5)  consecutive  trading
days  ending one  trading  day prior to the Second  Anniversary  Date;  Series A
Preferred Shares converted on or after the Third Anniversary Date and before the
Fourth Anniversary Date are convertible at a per share conversion price equal to
the  Average  Market  Price of the  Common  Stock  for the five (5)  consecutive
trading days ending one trading day prior to the Third  Anniversary Date; Series
A Preferred Shares converted on or after the Fourth  Anniversary Date and before
January 1, 2003 are convertible at a per share  conversion price equal to 88% of
the  Average  Market  Price of the  Common  Stock  for the five (5)  consecutive
trading days ending one trading day prior to the Fourth  Anniversary  Date;  and
Series A Preferred  Shares converted on or after January 1, 2003 are convertible
at a per share  conversion price equal to the Average Market Price of the Common
Stock for the five (5) consecutive  trading days ending one trading day prior to
the receipt by the Company of a notice of conversion.  For purposes of computing
the conversion price,  "Average Market Price" of the Common Stock for any period
is the average of the closing  prices for the Common  Stock for each trading day
in such period as reported by the NASDAQ  National  Market or any trading system
on which the Common Stock may then be quoted. The conversion price is subject to
adjustment in the case of certain  


                                       8
<PAGE>

dilutive  events.  Further,  in the event the Average Market Price of the Common
Stock for the five (5) consecutive  trading days ending one trading day prior to
any  trading  day during  which any Series A  Preferred  Shares are  outstanding
exceeds 150% of the conversion  price then in effect,  the Company has the right
to  require  the  holder of the Series A  Preferred  Shares to convert  all such
shares as may then be convertible. In connection with the issuance of the Series
A Preferred Shares,  Merck was granted certain  registration rights with respect
to the underlying  shares of Common Stock.  Due to the fact that,  commencing on
the Second  Anniversary  Date,  the number of shares of Common  Stock into which
Series A Preferred  Shares are convertible is not fixed,  and is determined with
reference to the market prices of the Company's Common Stock as described above,
as the market price of the Common Stock decreases, the number of shares issuable
upon conversion of the Series A Preferred Shares will increase.

      Limited Manufacturing Experience.

      To  be  successful,   the  Company's  products  must  be  manufactured  in
commercial  quantities  in  compliance  with  regulatory   requirements  and  at
acceptable costs.  Although the Company has developed products in the laboratory
and  in  some  cases  has  produced  sufficient   quantities  of  materials  for
pre-clinical  animal trials and early stage clinical trials,  production in late
stage clinical or commercial  quantities may create technical challenges for the
Company.  The  Company  owns a  facility  which  is used  as its  clinical-scale
manufacturing facility. If it commercializes its products, the Company may adapt
this facility or outfit an additional  facility for use as its  commercial-scale
manufacturing   facility.   However,  the  Company  has  limited  experience  in
clinical-scale    manufacturing   and   no   experience   in    commercial-scale
manufacturing,  and no  assurance  can be given that the Company will be able to
make the transition to late stage clinical or commercial production.  The timing
and any  additional  costs of adapting the  Company's  facility or outfitting an
additional facility for commercial manufacturing will depend on several factors,
including the progress of products through clinical trials,  and such timing and
additional costs are not yet determinable.

      Establishing Sales and Marketing Capability.

      As  a  research  and  development  company,  the  Company  does  not  have
significant  experience  in selling or marketing  new  products.  The  Company's
current strategy does not necessarily  include marketing products on its own, as
it may do so initially through,  or in conjunction with, its corporate partners.
See "Risk  Factors-Dependence  on Certain Contractual  Agreements with Corporate
Partners.  " At such time as the Company seeks to market directly a new product,
the Company  will  require  expertise  in sales and  marketing.  There can be no
assurance that the Company will be able to retain qualified or experienced sales
and marketing personnel or that any efforts undertaken by such personnel will be
successful.  Under the Company's agreement with Merck, the Company has the right
to  co-market  BEC2 in North  America in the event BEC2 is approved  for sale in
North America.

      Dependence on Certain Contractual Agreements with Corporate Partners.

      To date,  the  Company  has  derived  substantially  all,  and the Company
expects to continue to derive over the next several years a substantial portion,
of its  revenues  related to research  and  development  funding and license fee
revenues from agreements with corporate  partners.  These  agreements  typically
provide the corporate  partner with certain rights to manufacture  and/or market
in certain  geographic  areas  specified  products which are developed using the
Company's proprietary  technology,  subject to an obligation to pay royalties to
the Company based on future product sales, if any.  Certain of these  agreements
provide for funding by corporate  partners of research  activities  performed by
the  Company,  and in some cases for  payments to the  Company of license  fees,
either upon  entering  into such  agreements  or upon  achievement  of specified
research,  regulatory and commercialization  milestones,  or both. The Company's
revenues  from these  agreements  are not  received at regular  intervals,  have
fluctuated in the past, and are expected to continue to fluctuate in the future.
In general,  the  agreements  from which the Company  derives such  revenues are
subject to early  termination at the election of the corporate  partner.  In the
past, some of these  arrangements  have been  terminated.  There is no assurance
that revenues from these  sources will be  maintained,  or that the Company will
enter into any additional agreements of a similar nature.

      Under  most of these  agreements,  the  corporate  partner,  at least  for
certain  territories,  controls and is responsible for the design and conduct of
pre-clinical and clinical trials, seeking and obtaining of regulatory approvals,
establishing  clinical  and  commercial-scale   manufacturing  capabilities  and
manufacturing and marketing of products in those  territories.  Pursuant to such
agreements,  the  amount  and  timing of  funding  and the  investment  of other
resources are  controlled by such other parties 


                                       9
<PAGE>

and also are subject to the risk of  financial  or other  difficulties  that may
befall such other  parties.  In addition,  the Company's  corporate  partners or
their affiliates may be pursuing alternative products or technologies addressing
the same purposes as those which are the subject of their collaboration with the
Company.  While the Company believes its corporate partners have or will have an
economic  motivation  to  succeed in  performing  their  obligations  under such
agreements,  there  can  be  no  assurance  that  the  corporate  interests  and
motivations of these partners will remain consistent with those of the Company.

      Uncertainties as to Patents and Proprietary Technologies.

      The patent  position of  biopharmaceutical  companies  generally is highly
uncertain  and  involves  complex  legal and factual  questions.  The  Company's
success  will  depend,  in part,  on its  ability  to obtain  patents on its own
products,  obtain  licenses to use third  parties'  technologies,  protect trade
secrets, and operate without infringing the proprietary rights of others. If the
Company is unable to obtain patents that adequately protect its own products, or
if any of the  Company's  proprietary  technologies  were to  conflict  with the
rights of others,  the Company's  ability to  commercialize  products using such
technologies could be materially and adversely affected.

      The Company  currently is the exclusive  licensee or assignee of 42 issued
patents worldwide,  24 of which are issued United States patents. The Company is
the  assignee  or  exclusive  licensee  of  approximately  36 families of patent
applications  in the  United  States and in foreign  countries  directed  to its
proprietary  technology.  There can be no assurance that patents will issue as a
result of any of such  applications.  Nor can there be any assurance that issued
patents would be of substantial  protection or commercial benefit to the Company
or would afford the Company  adequate  protection from competing  products.  For
example,  issued  patents may be challenged and declared  invalid.  In addition,
under many of its license agreements with third parties, the Company is required
to meet  specified  milestone or diligence  requirements  in order to retain its
license to such third  party  patents and patent  applications.  There can be no
assurance that the Company will satisfy any of these requirements.

      The  Company  holds  rights  under  certain  third party  patents  that it
considers  necessary for the  development of its  technology.  It is anticipated
that,  in order to  commercialize  certain of the  products  that the Company is
developing  or may  develop,  the Company  may be required to obtain  additional
licenses  to  patents  from  third  parties.  However,  the extent to which such
licenses may be required, the availability of such licenses and the cost of such
licenses, if they are available, are uncertain, at present.

      The Company is aware that other parties have filed patent  applications in
various countries in several areas in which the Company is developing  products.
Some of these  patent  applications  have  issued as patents  and some are still
pending. There can be no assurance that the pending patent applications will not
issue as patents.  Issued  patents are entitled to a rebuttable  presumption  of
validity under the laws of the United States and certain other countries.  These
issued  patents  may  adversely  affect the  ability  of the  Company to develop
commercial products it is attempting to develop. If licenses to such patents are
needed,  there can be no assurance that any such licenses would be obtainable by
the Company on acceptable terms.

      The  following are some of the areas in which the Company may be adversely
affected by the patents and patent applications of others:

      The Company  has an  exclusive  license to an issued  U.S.  patent for the
murine form of C225, the Company's EGFr antibody product. The Company's licensor
did not seek patent  protection  outside the United  States with respect to this
antibody.  Outside the United States, the Company is relying, in part, on patent
applications  exclusively  licensed  from a major  pharmaceutical  company which
claim the use of an EGFr antibody in conjunction with  chemotherapeutic  agents.
The  Company  is  currently  prosecuting  these  applications.  There  can be no
assurance that the Company will be successful in these efforts.

      The  EGFr  antibody  being  developed  by the  Company  is a  "chimerized"
monoclonal antibody.  Patents have been issued to other biotechnology  companies
that cover the  chimerization of antibodies,  and the Company may be required to
obtain  licenses  under these patents in order to  commercialize  its chimerized
monoclonal  antibodies.  There can be no assurance that the Company will be able
to obtain such licenses in the territories where it proposes commercialization.

      The  Company is aware that  third-party  patents  have been  issued in the
United States and Europe covering anti-idiotypic antibodies and/or their use for
the treatment of tumors. Such patents, if valid, could be construed to cover the
Company's BEC2 monoclonal antibody and certain uses thereof in the United States
and most of Europe. Merck, the Company's licensee of BEC2 worldwide (except that
the Company has retained the right to co-promote BEC2 in the United States), has
informed the Company that it has obtained a non-exclusive,  worldwide license to
such patent in order to market 


                                       10
<PAGE>

BEC2 in its  territory.  No assurance  can be given that such  license  would be
available to the Company in other parts of the world on commercially  acceptable
terms, if at all.

      The   Company   maintains  a   proprietary   position   with   respect  to
anti-angiogenic  therapeutics,  as  well  as  therapeutic  methods  of  treating
angiogenic  disease,  through  patents  and  patent  applications  filed  by the
Company.  The Company is aware that third parties have filed patent applications
that could  affect  the  ability of the  Company  to  commercialize  some of its
anti-angiogenic therapeutics or therapeutic treatments.

      The United Sates Patent and  Trademark  Office has granted two patents for
the Company's  cysteine-depleted IL-6 molecular variant, IL-6m, and the DNA that
encodes IL-6m.  The patent and patent  applications  are co-owned by the Company
and the  University  of North  Carolina,  whose  rights  have  been  exclusively
licensed to the Company. The Company is aware of patents issued to a third party
in  the  United  States  and  Europe  covering  cysteine-depleted  proteins.  In
addition,  the Company is aware of third-party  patents for both recombinant and
native IL-6 and methods for its  production.  The Company is aware of a European
patent for the DNA  encoding  for human  recombinant  IL-6 and  methods  for its
production  which  has  been  exclusively  licensed  on a  worldwide  basis to a
pharmaceutical company. The Company has entered into a settlement agreement with
such pharmaceutical company whereby the pharmaceutical company has agreed not to
enforce its patent  against the Company  based on the Company's use of its IL-6m
patent or patent applications.

      The Company is aware that third parties have filed patent  applications in
areas  that  could  affect  the  ability  of the  Company  or its  licensee  for
diagnostics,  Abbott, to commercialize the Company's diagnostic products.  These
areas could include target  amplification  technology  and signal  amplification
technology.  Third  party  patents  have  already  issued in the field of target
amplification such as polymerase chain reaction technology (also known as PCR).

      There has been significant  litigation in the  biopharmaceutical  industry
regarding  patents and other  proprietary  rights.  Such litigation has consumed
substantial  resources for the parties involved.  If the Company became involved
in similar  litigation  regarding its intellectual  property rights, the cost of
such litigation could be substantial and could have a material adverse effect on
the Company.

      Certain proprietary trade secrets and unpatented know-how are important to
the Company in conducting its research and development activities.  There can be
no  assurance  that  others may not  independently  develop  the same or similar
technologies.  Although the Company has taken  steps,  including  entering  into
confidentiality  agreements with its employees and third parties, to protect its
trade secrets and unpatented know-how, third parties nonetheless may gain access
to such information.

      Reliance on and Attraction and Retention of Key Personnel and Consultants.

      The Company's ability to successfully  develop marketable  products and to
maintain a  competitive  position  will  depend in large part on its  ability to
attract and retain highly qualified  scientific and management  personnel and to
develop and  maintain  relationships  with  leading  research  institutions  and
consultants.  The Company is highly dependent upon the principal  members of its
management, scientific staff and Scientific Advisory Board. Competition for such
personnel and  relationships is intense,  and there can be no assurance that the
Company will be able to continue to attract and retain such personnel.

      Technological Change and Risk of Obsolescence; Competition.

      The  biopharmaceutical  industry  is  subject  to  rapid  and  significant
technological  change.  The Company has numerous  competitors,  including  major
pharmaceutical  and  chemical  companies,   specialized   biotechnology   firms,
universities and other research  institutions.  These competitors may succeed in
developing  technologies and products that are more effective than any which are
being  developed by the Company or which would render the  Company's  technology
and  products  obsolete  and  non-competitive.  Many of these  competitors  have
substantially  greater  financial and technical  resources  and  production  and
marketing  capabilities  than the Company.  In addition,  many of the  Company's
competitors  have   significantly   greater   experience  than  the  Company  in
pre-clinical testing and human clinical trials of new or improved pharmaceutical
products  and in  obtaining  Food  and Drug  Administration  ("FDA")  and  other
regulatory approvals on products for use in health care. The Company is aware of
various products under  development or manufactured by competitors that are used
for the prevention,  diagnosis or treatment of certain  diseases the Company has
targeted for product development,  some of which use therapeutic approaches that
compete directly with certain of the Company's product  candidates.  The Company
has limited  experience  in  


                                       11
<PAGE>

conducting and managing the pre-clinical testing necessary to enter the clinical
trials  that are  required  to  obtain  government  approvals,  and has  limited
experience in conducting clinical trials. Accordingly, the Company's competitors
may succeed in  obtaining  FDA  approval  for  products  more  rapidly  than the
Company,  which could adversely affect the Company's  ability to further develop
and market its products. If the Company commences  significant  commercial sales
of its  products,  it will  also be  competing  with  respect  to  manufacturing
efficiency and marketing capabilities, areas in which the Company has limited or
no experience.

      Extensive Government Regulation.

      Research, pre-clinical development,  clinical trials and the manufacturing
and marketing of therapeutic  and diagnostic  products under  development by the
Company  are  subject to  extensive  and  rigorous  regulation  by  governmental
authorities in the United States and other  countries.  Clinical  trials and the
manufacturing  and  marketing  of  products  will be subject to the  testing and
approval processes of the FDA and comparable foreign regulatory authorities. The
process  of  obtaining  such  required  regulatory  approvals  for the  types of
products  under  development  by the  Company  usually  takes  many years and is
expensive.  Development  of a new biologic  therapeutic  or vaccine  product may
take, from initiation of clinical trials until FDA approval,  an average of five
to ten years (or more), while in vitro diagnostics may take approximately two to
six years, or more,  depending on the  requirements  of the approval  process or
clinical data  requirements.  If the FDA requests  additional  data,  these time
periods can be  substantially  increased.  Even after such  additional  data are
submitted,  there can be no assurance of obtaining  FDA  approval.  In addition,
product approvals may be withdrawn or limited for noncompliance  with regulatory
standards or the occurrence of unforeseen  problems following initial marketing.
The Company has not sought or received  regulatory  approval for the  commercial
sale of any of its products or for any  manufacturing  processes or  facilities.
The Company and its  licensees  may  encounter  significant  delays or excessive
costs in their  respective  efforts to secure  necessary  approvals or licenses.
Future federal, state, local or foreign legislative or administrative acts could
also prevent or delay  regulatory  approval of the  Company's or its  licensees'
products.  There  can be no  assurance  that the  Company  or its  collaborative
partners  will be able to obtain the necessary  approvals for clinical  testing,
manufacturing or marketing of the Company's products,  or that the clinical data
they obtain in clinical  studies will be  sufficient to establish the safety and
effectiveness  of  the  products.   Failure  to  obtain  or  maintain  requisite
governmental  approvals or failure to obtain approvals of the clinical  intended
uses  requested,  could delay or  preclude  the  Company or its  licensees  from
further developing particular products or from marketing their products or could
limit the  commercial  use of the products  and thereby have a material  adverse
effect on the Company's liquidity and financial condition.

      Product Liability Exposure.

      The use of the  Company's  product  candidates  during  testing  or  after
approval  entails an inherent  risk of adverse  effects  which could  expose the
Company to product liability claims.  There can be no assurance that the Company
would have sufficient resources to satisfy any liability resulting from any such
claims.  The  Company  endeavors  to  obtain  indemnification  by its  corporate
partners against certain of such claims. However, there can be no assurance that
such  parties will honor,  or have the  financial  resources to honor,  any such
obligations.  The Company currently has product liability insurance which covers
products in pre-clinical  and clinical  testing.  There can be no assurance that
such coverage will be adequate in scope to protect the Company in the event of a
successful product liability claim.

      Hazardous Materials; Environmental Matters.

      The Company's  research and development  activities involve the controlled
use  of  hazardous  materials,   chemicals,   viruses  and  various  radioactive
compounds.  The  Company  is  subject  to  federal,  state  and  local  laws and
regulations  governing the use, manufacture,  storage,  handling and disposal of
such materials and certain waste  products.  Although the Company  believes that
its safety  procedures for handling and disposing of such materials  comply with
the standards  prescribed by such laws and  regulations,  the risk of accidental
contamination or injury from these materials cannot be completely eliminated. In
the event of such an accident,  the Company could be held liable for any damages
that result,  and any such liability  could exceed the resources of the Company.
The  Company  may  be  required  to  incur  significant  costs  to  comply  with
environmental  laws and  regulations  in the future.  The Company's  operations,
business or assets may be materially or adversely  affected by current or future
environmental laws or regulations.


                                       12
<PAGE>

      Uncertainty of Health Care Reimbursement and Related Matters.

      The  Company's  ability to earn  sufficient  returns on its  products  may
depend  in part on the  extent  to  which  reimbursement  for the  costs of such
products and related treatments will be available to purchasers or users thereof
from  government  health  administration  authorities,  private health  coverage
insurers  and  other  organizations.  If  purchasers  or users of the  Company's
products are not entitled to adequate  reimbursement  for the cost of using such
products,  they may forego or reduce such use. Significant uncertainty exists as
to the  reimbursement  status of newly approved health care products,  and there
can be no assurance that adequate third-party coverage will be available.

      Possible Volatility of Stock Price.

      The Company  believes  that  factors such as the status of its products in
development,   announcements  of  new  products,  formation  or  termination  of
corporate  alliances,  other developments by the Company, its competitors or the
FDA,  determinations  in connection  with patent  applications of the Company or
others and variations in quarterly operating results,  among others, could cause
the market price for the Common Stock to fluctuate  substantially.  In addition,
the stock market has experienced extreme price and volume fluctuations that have
particularly   affected   the  market  price  for  many  high   technology   and
healthcare-related companies and that have often been unrelated to the operating
performance of these  companies.  These broad market  fluctuations may adversely
affect the market price of the Common Stock.

      Limitations on Net Operating Loss Carryforwards.

      At December 31, 1997, the Company had net operating loss carryforwards for
federal  income tax  purposes  of  approximately  $115,000,000  which  expire at
various  dates from 2000  through  2012.  At  December  31, 1997 the Company had
research  credit  carryforwards  of  approximately  $2,303,000  which  expire at
various  dates from 2001 through  2012.  Pursuant to Section 382 of the Internal
Revenue Code of 1986,  as amended,  the annual  utilization  of a company's  net
operating loss and research credit  carryforwards may be limited if such company
experiences  a change in ownership of more than 50  percentage  points  within a
three-year  period.  Since 1986, the Company has  experienced two such ownership
changes.  Accordingly,  the Company's net operating loss carryforwards available
to offset future federal  taxable  income arising before such ownership  changes
are limited to  $5,159,000  annually.  Similarly,  the Company is  restricted in
using its research credit carryforwards arising before such ownership changes to
offset future federal income tax expense.

      Dividend Policy and Restrictions.

      The Company has never paid any cash  dividends  on its Common  Stock.  The
Board of Directors of the Company will determine future dividend policy based on
the Company's results of operations,  financial condition,  capital requirements
and other circumstances. The Company does not anticipate that any dividends will
be  declared on its Common  Stock in the  foreseeable  future.  Except as may be
utilized to pay the dividends payable on the Company's Series A Preferred Stock,
any  earnings  which the  Company  may  realize  will be retained to finance the
growth of the Company.  In addition,  the terms of the Series A Preferred  Stock
restrict  the payment of  dividends  on other  classes and series of stock.  See
"Prospectus    Summary-The    Company-BEC2    Cancer    Vaccine"    and    "Risk
Factors-Dilution."

                                 USE OF PROCEEDS

      The  Company  will not receive  any  proceeds  from the sale of the Shares
offered herein by the Selling Stockholders, however, the Company has received or
will  receive the  exercise  price for Options  and  Warrants  upon the prior or
future exercise by such Selling  Stockholders  of such Options and Warrants.  If
all of the Options and Warrants held by Selling  Stockholders  as of the date of
this Prospectus and covered by this  Prospectus are exercised,  the Company will
receive  aggregate  estimated  proceeds  (including any amounts  received by the
Company in  connection  with the previous  exercise by Selling  Stockholders  of
Options and  Warrants  prior to the date of this  Prospectus)  of  approximately
$17,562,000.  The Company anticipates utilizing any such proceeds received,  and
has utilized any such proceeds  previously  received,  upon the exercise of such
Options  and  Warrants  (i) to  continue  to fund and  expand its  research  and
development programs and (ii) for general corporate purposes,  including working
capital. There can be no assurance that any of the Options will be exercised.


                                       13
<PAGE>

                              SELLING STOCKHOLDERS

      This Prospectus covers possible sales by the Selling Stockholders, who are
officers and directors of the Company who may be "affiliates" of the Company (as
such term is defined  under Rule 405 under the  Securities  Act), of Shares that
such Selling  Stockholders have acquired and/or may acquire through the exercise
of Options granted under the Plans and/or  Warrants.  The names of such officers
and  directors  who may be  Selling  Stockholders  from time to time are  listed
below,  along with, as of September 25, 1998, (i) the number of shares of Common
Stock currently owned by each such person,  (ii) the number of Shares offered by
each such person for sale hereby and (iii) the number of shares of Common  Stock
to be owned by each such Selling  Stockholder  following  the  completion of the
offering  contemplated  hereby and the percentage  that such shares will bear to
the number of  outstanding  shares of Common  Stock at such time.  The number of
Shares  offered for sale by such  individuals  may be updated in, and additional
individuals  who  are  affiliates  of  the  Company  may  be  added  as  Selling
Stockholders  hereunder by, supplements to this Prospectus,  which will be filed
with the Commission in accordance  with Rule 424(b) under the Securities Act. In
reliance  upon  Item  2(b) of  General  Instruction  C to  Form  S-8  under  the
Securities  Act,  the  officers  and  directors  of the Company  listed below as
Selling  Stockholders have been listed herein whether or not such persons have a
present  intent to reoffer or resell any or all of the Shares listed as owned by
them and being offered hereby.

                                                       Number       Percentage 
                                                     of Shares       of Shares
                         Number           Number    Beneficially   Beneficially
                        of Shares       of Shares   Owned After    Owned After 
                       Beneficially      Offered    Completion of Completion of
Selling Stockholder(1)   Owned(2)       Hereby(3)    Offering(4)    Offering(4)
----------------------   --------       ---------    -----------    -----------

Richard Barth             41,500(5)       40,000(5)      1,500          *   
                                                                        
Dr. Jean Carvais          48,542(6)       48,542(6)          0          *
                                                                        
Vincent T. DeVita, Jr     90,842(7)       90,542(7)        300          *
                                                                        
Robert F. Goldhammer     836,576(8)      183,232(8)    653,344          2.41%
                                                                        
Carl S. Goldfischer      375,000(9)      375,000(9)          0          *
                                                                        
David M. Kies           107,000(10)      41,397(10)     65,603          *
                                                                        
Paul B. Kopperl          70,960(11)      49,960(11)     21,000          *
                                                                        
John Mendelsohn         212,226(12)     212,226(12)          0          *
                                                                        
William Miller           42,397(13)      41,397(13)      1,000          *
                                                                        
Harlan Waksal         1,245,780(14)     411,578(14)    834,202          3.07%
                                                                        
Samuel Waksal         1,467,583(15)   1,359,000(15)    108,583          *
                                                                     
----------
*     Less than 1%.

(1)   Notwithstanding  their  respective  inclusion  in this  table  as  Selling
      Stockholders, the individuals listed in this table expressly disclaim that
      they are affiliates of the Company.

(2)   Assumes that all options or warrants to acquire  Common Stock held by such
      Selling  Stockholder  are  exercisable  within 60 days of the date of this
      Prospectus.

(3)   Assumes that all Options and Warrants held by such Selling Stockholder are
      fully exercisable for the underlying Shares.

(4)   Assumes the sale of all Shares offered by all Selling  Stockholders  under
      this Prospectus, and that all options and warrants to acquire Common Stock
      held by such Selling  Stockholders  are exercisable  within 60 days of the
      date of the  completion of the offering.  As the Company is unable,  as of
      the date of this  Prospectus,  to determine the date of the  completion of
      the  offering  hereunder,  the  number of  shares  and  percentages  shown
      hereunder are computed with reference to the aggregate number of shares of
      Common Stock of the Company  issued and  outstanding  as of September  25,
      1998 and giving effect to the exercise of the Options and Warrants. Shares
      of the Company's Series A Convertible Preferred Stock are not included, as
      no voting rights are attached to such shares.


                                       14
<PAGE>

(5)      Includes an aggregate of 40,000  Shares  subject to Options  granted to
         Mr.  Barth   pursuant  to  the  ImClone   Systems   Incorporated   1996
         Non-Qualified Stock Option Plan. Mr. Barth is a director of the Company

(6)      Includes (i) an aggregate of 20,542 Shares  subject to Options  granted
         to Dr.  Carvais  pursuant  to the  ImClone  Systems  Incorporated  1986
         Non-Qualified  Stock Option Plan and (ii) an aggregate of 28,000 Shares
         subject  to Options  granted to Dr.  Carvais  pursuant  to the  ImClone
         Systems  Incorporated 1996 Non-Qualified Stock Option Plan. Dr. Carvais
         is a director of the Company.

(7)      Includes (i) an aggregate of 48,542 Shares  subject to Options  granted
         to  Dr.  DeVita  pursuant  to the  ImClone  Systems  Incorporated  1986
         Non-Qualified  Stock  Option Plan,  (ii) an aggregate of 20,000  Shares
         previously  acquired by Mr. DeVita upon the exercise of Options granted
         thereto pursuant to the ImClone Systems Incorporated 1986 Non-Qualified
         Stock Option Plan,  and (iii) an aggregate of 22,000 Shares  subject to
         Options   granted  to  Mr.  DeVita  pursuant  to  the  ImClone  Systems
         Incorporated  1996  Non-Qualified  Stock Option Plan.  Dr.  DeVita is a
         director of the Company.

(8)      Includes (i) an aggregate of 8,542 Shares subject to Options granted to
         Mr.  Goldhammer  pursuant  to the  ImClone  Systems  Incorporated  1986
         Non-Qualified  Stock Option Plan,  (ii) an aggregate of 105,000  Shares
         subject to Options  granted to Mr.  Goldhammer  pursuant to the ImClone
         Systems  Incorporated 1996 Non-Qualified Stock Option Plan and (iii) an
         aggregate  of  69,690  Shares   subject  to  Warrants   issued  to  Mr.
         Goldhammer.  The  additional  shares of Common  Stock  listed under the
         column "Number of Shares  Beneficially  Owned" include 13,314 shares of
         Common  Stock  held in  trust,  as to which  Mr.  Goldhammer  disclaims
         beneficial  ownership.  Mr. Goldhammer is the Chairman of the Company's
         Board of Directors.

(9)      Includes (i) an aggregate of 350,000 Shares subject to Options  granted
         to Dr.  Goldfischer  pursuant to the ImClone Systems  Incorporated 1996
         Non-Qualified  Stock Option Plan and (ii) an aggregate of 25,000 Shares
         subject to Options granted to Dr.  Goldfischer  pursuant to the ImClone
         Systems  Incorporated 1996 Incentive Stock Option Plan. Dr. Goldfischer
         is the Company's Vice President, Finance and Chief Financial Officer.

(10)     Includes (i) an aggregate of 25,000 Shares  subject to Options  granted
         to  Mr.  Kies  pursuant  to  the  ImClone  Systems   Incorporated  1996
         Non-Qualified  Stock Option Plan and (ii) an aggregate of 16,397 Shares
         previously  acquired by Mr. Kies upon the  exercise of Options  granted
         thereto pursuant to the ImClone Systems Incorporated 1996 Non-Qualified
         Stock Option Plan. The  additional  shares of Common Stock listed under
         the column "Number of Shares  Beneficially  Owned" include 6,000 shares
         of Common Stock held by Mr. Kies as custodian  for his son, as to which
         Mr. Kies disclaims beneficial ownership.  Mr. Kies is a director of the
         Company.

(11)     Includes (i) an aggregate of 7,500 Shares subject to Options granted to
         Mr.  Kopperl  pursuant  to  the  ImClone  Systems   Incorporated   1986
         Non-Qualified  Stock Option Plan and (ii) an aggregate of 40,000 Shares
         subject  to Options  granted to Mr.  Kopperl  pursuant  to the  ImClone
         Systems   Incorporated  1996  Non-Qualified   Stock  Option  Plan.  The
         additional  shares of Common Stock  listed under the column  "Number of
         Shares  Beneficially  Owned" include 500 shares of Common Stock held by
         Mr.  Kopperl's  spouse as to which  Mr.  Kopperl  disclaims  beneficial
         ownership. Mr. Kopperl is a director of the Company.

(12)     Includes (i) an aggregate of 120,000 Shares subject to Options  granted
         to Dr.  Mendelsohn  pursuant to the ImClone Systems  Incorporated  1986
         Non-Qualified  Stock Option Plan and (ii) an aggregate of 92,226 Shares
         subject to Options  granted to Dr.  Mendelsohn  pursuant to the ImClone
         Systems   Incorporated  1996  Non-Qualified   Stock  Option  Plan.  Dr.
         Mendelsohn is a director of the Company.

(13)     Includes an aggregate of 41,397  Shares  subject to Options  granted to
         Mr.  Miller   pursuant  to  the  ImClone  Systems   Incorporated   1996
         Non-Qualified  Stock  Option  Plan.  Mr.  Miller is a  director  of the
         Company.

(14)     Includes (i) an aggregate of 390,000 Shares subject to Options  granted
         to  Dr.  Waksal  pursuant  to the  ImClone  Systems  Incorporated  1996
         Non-Qualified  Stock Option Plan and the ImClone  Systems  Incorporated
         1996  Incentive  Stock Option  Plan,  (ii) an aggregate of 3,180 Shares
         subject to  Warrants  issued to Dr.  Waksal and (iii) an  aggregate  of
         18,398  Shares  previously  acquired by Dr. Waksal upon the exercise of
         Options  granted thereto  pursuant to the ImClone Systems  Incorporated
         1986  Non-Qualified  Stock  Option  Plan.  Dr.  Harlan  Waksal  is  the
         Company's  Executive Vice President and Chief  Operating  Officer and a
         director of the Company.  Dr.  Harlan  Waksal and Dr. Samuel Waksal are
         brothers.

(15)     Includes (i) an aggregate of 75,000 Shares  subject to Options  granted
         to  Dr.  Waksal  pursuant  to the  ImClone  Systems  Incorporated  1986
         Non-Qualified  Stock Option Plan,  (ii) an aggregate of 595,000  Shares
         subject to Options granted


                                       15
<PAGE>

         to  Dr.  Waksal  pursuant  to the  ImClone  Systems  Incorporated  1996
         Non-Qualified  Stock Option Plan and the ImClone  Systems  Incorporated
         1996 Incentive Stock Option Plan,  (iii) an aggregate of 350,000 Shares
         subject  to  Warrants  issued to Dr.  Waksal and (iv) an  aggregate  of
         339,000 Shares  previously  acquired by Dr. Waksal upon the exercise of
         Warrants issued thereto.  Dr. Samuel Waksal is the Company's  President
         and Chief  Executive  Officer.  Dr. Samuel Waksal and Dr. Harlan Waksal
         are brothers.

                              PLAN OF DISTRIBUTION

      The Shares,  which have been issued  and/or are issuable upon the exercise
of the  Options or  Warrants  may be sold  pursuant  to this  Prospectus  by the
Selling Stockholders. These sales may occur in privately negotiated transactions
or in the over-the-counter  market through brokers and dealers, as agents, or to
brokers and dealers,  as principals who may receive  compensation in the form of
discounts,  concessions or commissions from the Selling Stockholders or from the
purchasers of the Common Stock for whom the  broker-dealers  may act as agent or
to whom they may sell as principal,  or both. After the passage of the requisite
period of time, the Selling  Stockholders  may also sell the Shares  pursuant to
Rule 144.  The Company has been  advised by the Selling  Stockholders  that they
have not made any arrangements  relating to the  distribution of the Shares.  In
effecting sales,  broker-dealers  engaged by the Selling Stockholder may arrange
for other broker-dealers to participate. Broker-dealers will receive commissions
or  discounts  from  the  Selling   Stockholder  in  amounts  to  be  negotiated
immediately prior to the sale.

      Upon being notified by a Selling Stockholder that any material arrangement
(other than a customary  brokerage account agreement) has been entered into with
a broker or dealer for the sale of Shares pursuant to this Prospectus  through a
block trade, purchase by a broker or dealer, or similar transaction, the Company
will file a supplemented Prospectus pursuant to Rule 424(c) under the Securities
Act disclosing (a) the name of each such broker-dealer, (b) the number of Shares
involved, (c) the price at which such Shares were sold, (d) the commissions paid
or discounts or concessions allowed to such broker-dealer(s), (e) if applicable,
that such  broker-dealer(s)  did not  conduct  any  investigation  to verify the
information  set  out  or  incorporated  by  reference  in  the  Prospectus,  as
supplemented, and (f) any other facts material to the transaction.

      The Selling  Stockholders and any broker-dealers who execute sales for the
Selling  Stockholders may be deemed to be  "underwriters"  within the meaning of
the  Securities Act by virtue of the number of shares of Common Stock to be sold
or resold by such persons or entities or the manner of sale thereof, or both. If
the Selling  Stockholders or any  broker-dealer or other holders were determined
to be underwriters,  any discounts,  concessions or commissions received by them
or by brokers or dealers acting on their behalf and any profits received by them
on the  resale  of their  shares of Common  Stock  might be deemed  underwriting
discounts and commissions under the Securities Act.

      The Selling Stockholders have represented to the Company that any purchase
or sale of the Common  Stock by them will be in  compliance  with  Regulation  M
("Regulation M") promulgated under the Exchange Act. In general,  Rule 102 under
Regulation M prohibits any person connected with a distribution of the Company's
Common Stock (the  "Distribution")  from directly or indirectly  bidding for, or
purchasing  for any account in which he has a  beneficial  interest,  any Common
Stock or any right to purchase  Common  Stock,  for a period of one business day
prior to and subsequent to completion of his  participation  in the Distribution
(the "Distribution Period").

      During the Distribution  Period,  Rule 104 ("Rule 104") under Regulation M
prohibits  the  Selling  Stockholders  and  any  other  persons  engaged  in the
Distribution from engaging in any stabilizing bid or purchasing the Common Stock
except for the purpose of  preventing  or retarding a decline in the open market
price of the Common Stock. No such person may effect any stabilizing transaction
to facilitate  any offering at the market.  Inasmuch as any Selling  Stockholder
will be  reoffering  and  reselling  the Common  Stock at the  market,  Rule 104
prohibits him or her from effecting any stabilizing transaction in contravention
of Rule 104 with respect to the Common Stock.

                                  LEGAL MATTERS

      Certain  legal  matters in  connection  with the sale and  validity of the
Shares  will be passed upon for the Company by Kaye,  Scholer,  Fierman,  Hays &
Handler, LLP.



                                       16
<PAGE>

                      DISCLOSURE OF COMMISSION POSITION ON
                 INDEMNIFICATION FOR SECURITIES ACT LIABILITIES

      The  Company's   Certificate  of  Incorporation  and  Bylaws  provide  for
indemnification  of officers and directors in instances,  among others, in which
they acted in good faith and in a manner they  reasonably  believed to be in, or
not opposed to, the best interests of the Company and in which,  with respect to
criminal proceedings,  they had no reasonable cause to believe their conduct was
unlawful.

      Insofar as  indemnification  for liabilities  arising under the Securities
Act of 1933 may be permitted to directors,  officers and controlling  persons of
the Company pursuant to the foregoing provisions,  or otherwise, the Company has
been  advised  that in the opinion of the  Commission  such  indemnification  is
against  public  policy as expressed in the  Securities  Act and is,  therefore,
unenforceable.


                                       17
<PAGE>

                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

      The   contents  of  ImClone   Systems   Incorporated's   (the   "Company")
Registration Statement on Form S-8, File No.333-10275, filed with the Securities
and Exchange  Commission (the  "Commission") on August 15, 1996 are incorporated
herein by reference.

Item 8.       Exhibits.

Exhibit No.   Description
-----------   -----------

5.1           Opinion  of  Kaye,  Scholer,  Fierman,  Hays &  Handler,  LLP with
              respect to the legality of the securities being registered. (Filed
              herewith).

23.1          Consent of KPMG Peat Marwick LLP. (Filed herewith).

23.2          Consent of Kaye, Scholer,  Fierman, Hays & Handler, LLP. (Included
              in Exhibit 5.1).

24.           Power  of  Attorney.   (Included   on  signature   pages  to  this
              Registration Statement).

99.1          ImClone Systems  Incorporated 1996 Incentive Stock Option Plan, As
              Amended. (Incorporated by reference to Exhibit No. 99.1 of ImClone
              Systems  Incorporated's  Quarterly  Report  of Form  10-Q  for the
              fiscal quarter ended June 30, 1997).

99.2          ImClone Systems Incorporated 1996 Non-Qualified Stock Option Plan,
              As Amended.  (Incorporated by reference to Exhibit 99.2 of ImClone
              Systems  Incorporated's  Quarterly  Reporting  Form  10-Q  for the
              fiscal quarter ended June 30, 1997).


                                       18
<PAGE>

                                   SIGNATURES

      Pursuant to the requirements of the Securities Act of 1933, the Registrant
certifies  that it has  reasonable  grounds to believe  that it meets all of the
requirements  for  filing  on Form S-8 and has  duly  caused  this  Registration
Statement  to be  signed  on its  behalf  by  the  undersigned,  thereunto  duly
authorized,  in the  City of New  York,  State of New  York,  on the 30th day of
September 1998.

                                  IMCLONE SYSTEMS INCORPORATED

                                  By: /s/  Samuel D. Waksal
                                      ----------------------------------------
                                      Samuel D. Waksal
                                      President and Chief Executive Officer

      Pursuant  to  the  requirements  of  the  Securities  Act  of  1933,  this
Registration  Statement  has been signed below by the  following  persons in the
capacities and on the dates indicated.  Each person whose  individual  signature
appears below hereby authorizes  Samuel D. Waksal,  Harlan W. Waksal and John B.
Landes, or any of them, to execute in the name and on behalf of each such person
and to file any amendment to this Registration Statement, and appoints Samuel D.
Waksal, Harlan W. Waksal and John B. Landes, or any of them, as attorney-in-fact
to sign on his behalf  individually  and in each capacity  stated below,  and to
file  any  amendments  to this  Registration  Statement,  including  any and all
post-effective amendments.

        Signature                     Title                          Date
        ---------                     -----                          ----

/s/  Robert F. Goldhammer    Chairman of the Board            September 30, 1998
-------------------------    and Director
Robert F. Goldhammer

/s/ Samuel D. Waksal         President, Chief Executive       September 30, 1998
-------------------------    Officer
Samuel D. Waksal             and Director
                             (Principal Executive Officer)

/s/  Harlan W. Walsal        Executive Vice President,        September 30, 1998
-------------------------    Chief Operating 
Harlan W. Waksal             Officer and Director

/s/  Carl Goldfischer        Vice President of Finance        September 30, 1998
-------------------------    and Chief Financial
Carl Goldfischer             Officer (Principal
                             Financial and Accounting 
                             Officer)

/s/  Jean Carvais            Director                         September 30, 1998
-------------------------
Jean Carvais

/s/ Vincent T. DeVita, Jr.   Director                         September 30, 1998
--------------------------
Vincent T. DeVita, Jr.

/s/  Paul B. Kopperl         Director                         September 30, 1998
-------------------------
Paul B. Kopperl

/s/  William R. Miller       Director                         September 30, 1998
-------------------------
William R. Miller

/s/  Davis M. Kies           Director                         September 30, 1998
-------------------------
David M. Kies

/s/  John Mendelsohn         Director                         September 30, 1998
-------------------------
John Mendelsohn

/s/  Richard Barth           Director                         September 30, 1998
-------------------------
Richard Barth


                                       S-1
<PAGE>

                                  EXHIBIT INDEX

Exhibit
No.                        Description
---                        -----------

5.1       Opinion of Kaye, Scholer, Fierman, Hays & Handler, LLP with respect to
          the legality of the securities being registered. (Filed herewith).

23.1      Consent of KPMG Peat Marwick LLP. (Filed herewith).

23.2      Consent of Kaye, Scholer,  Fierman,  Hays & Handler, LLP. (Included in
          Exhibit 5.1).

24.       Power of Attorney.  (Included on signature pages to this  Registration
          Statement).

99.1      ImClone  Systems  Incorporated  1996  Incentive  Stock Option Plan, As
          Amended.  (Incorporated  by  reference  to Exhibit No. 99.1 of ImClone
          Systems  Incorporated's  Quarterly  Report of Form 10-Q for the fiscal
          quarter ended June 30, 1997).

99.2      ImClone Systems  Incorporated 1996 Non-Qualified Stock Option Plan, As
          Amended. (Incorporated by reference to Exhibit 99.2 of ImClone Systems
          Incorporated's  Quarterly  Reporting  Form 10-Q for the fiscal quarter
          ended June 30, 1997).
[{"type": "S-8", "sequence": "1", "description": "FORM S-8", "secsgml_size_bytes": 106100}]
{"company-data": {"conformed-name": "IMCLONE SYSTEMS INC/DE", "cik": "0000765258", "assigned-sic": "2836", "irs-number": "042834797", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-64825", "film-number": "98718420"}, "business-address": {"street1": "180 VARICK ST", "city": "NEW YORK", "state": "NY", "zip": "10014", "phone": "2126451405"}, "mail-address": {"street1": "180 VARICK ST", "city": "NEW YORK", "state": "NY", "zip": "10014"}}
As filed with the Securities and Exchange Commission on September 30, 1998
                                                 Registration No.

================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                    FORM S-8

             REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933

                          IMCLONE SYSTEMS INCORPORATED
             (Exact name of registrant as specified in its charter)

            Delaware                                          04-2834797
   (State or other jurisdiction of                        (I.R.S. Employer      
    incorporation or organization)                        Identification No.)
                                                    
                                180 Varick Street
                            New York, New York 10014
               (Address of Principal Executive Offices) (Zip code)

    ImClone Systems Incorporated 1996 Incentive Stock Option Plan, As Amended
  ImClone Systems Incorporated 1996 Non-Qualified Stock Option Plan, As Amended
                            (Full title of the plan)

                                   ----------

                                 John B. Landes
            Vice President, Business Development and General Counsel
                          ImClone Systems Incorporated
                                180 Varick Street
                            New York, New York 10014
                     (Name and address of agent for service)

                                 (212) 645-1405
          (Telephone number, including area code, of agent for service)

                                    Copy to:
                           Lawrence A. Darby III, Esq.
                   Kaye, Scholer, Fierman, Hays & Handler, LLP
                                 425 Park Avenue
                          New York, New York 10022-3598

                         CALCULATION OF REGISTRATION FEE

================================================================================
Title of       Amount          Proposed maximum   Proposed maximum  Amount of 
securities to  to be           offering           aggregate         registration
be registered  registered(1)   price per share(2) offering price(2) fee
--------------------------------------------------------------------------------
Common Stock, 
$.001 par      
value .......     1,480 shares     $ 9.625          $    14,246        $    5
              1,161,726 shares       9.699           11,267,581         3,324
                336,794 shares       6.130            2,064,548           609
--------------------------------------------------------------------------------
   Totals ... 1,500,000 shares                      $13,346,375        $3,938
================================================================================

----------
(1)  Excludes such additional  indeterminate number of shares as may be issuable
     pursuant to the  anti-dilution  provisions of the Plans (as defined).  This
     total  represents an additional  1,500,000  shares of Common Stock,  in the
     aggregate,  reserved for issuance  pursuant to options granted or which may
     be  granted  under  either  of  the  ImClone  Systems   Incorporated   1996
     Non-Qualified  Stock  Option  Plan,  As  Amended,  or the  ImClone  Systems
     Incorporated  1996 Incentive Stock Option Plan, As Amended  (together,  the
     "Plans").  With  respect  to the Plans,  1,500,000  of the shares of Common
     Stock reserved for issuance  pursuant  thereto were  previously  registered
     pursuant to the Registrant's  Registration  Statement on Form S-8, File No.
     333-10275,  filed with the Securities and Exchange Commission on August 15,
     1996.

(2)  Estimated  solely for the purposes of  calculating  the  registration  fee.
     Pursuant to Rule 457(c) and Rule 457(h) under the  Securities  Act of 1933,
     as amended,  the proposed maximum offering price per share and the proposed
     maximum aggregate  offering price of shares subject to outstanding  options
     have  been  determined  based  on  the  average  exercise  prices  of  such
     outstanding options and shares not subject to outstanding options have been
     determined  based on the  average  of the high and low prices of the Common
     Stock on September 29, 1998, as reported by NASDAQ National Market.
REOFFER PROSPECTUS

                          IMCLONE SYSTEMS INCORPORATED

                                2,852,874 SHARES
                                 OF COMMON STOCK

      This Reoffer  Prospectus  (this  "Prospectus")  relates to the reoffer and
resale of an aggregate of 2,852,874  shares (the  "Shares") of the Common Stock,
par value $.001 per share (the "Common Stock"), of ImClone Systems  Incorporated
(the "Company" or the  "Registrant").  The Shares may be acquired,  or have been
acquired,  by certain officers and directors of the Company who may be deemed to
be  "affiliates" of the Company (as defined in Rule 405 under the Securities Act
of 1933,  as amended (the  "Securities  Act")),  all as  identified  herein (the
"Selling  Stockholders"),  from  time to time  upon the  exercise  of (A)  stock
options  ("Options")  granted as of the date of this Prospectus and/or which may
in the  future be  granted  to such  Selling  Stockholders  pursuant  to (i) the
ImClone  Systems  Incorporated  1996 Incentive Stock Option Plan and/or (ii) the
ImClone Systems  Incorporated 1996 Non-Qualified  Stock Option Plan and/or (iii)
the ImClone  Systems  Incorporated  1986 Incentive Stock Option Plan and/or (iv)
the  ImClone  Systems   Incorporated  1986   Non-Qualified   Stock  Option  Plan
(collectively,   the  "Plans")  and  (B)  certain  compensatory   warrants  (the
"Warrants")  to acquire  shares of the Common  Stock of the  Company  previously
issued by the Company to certain of its officers and directors.  The Company may
from time to time supplement  and/or amend this  Prospectus to cover  additional
shares of Common Stock that underlie  Options granted pursuant to one or more of
the Plans to "affiliates" of the Company.

      The Selling  Stockholders may, from time to time, offer all or part of the
Shares on the NASDAQ National Market or such national  securities  exchange upon
which  the  Common  Stock  may be  traded  at the  time of any  such  sales,  in
negotiated  transactions  or by a combination of these methods,  at fixed prices
that may be changed,  at market prices at the time of sale, at prices related to
market prices or at negotiated prices. The Selling Stockholders may effect these
transactions by selling the Shares to or through broker-dealers, who may receive
compensation in the form of discounts or commissions from a Selling Stockholder,
or from the purchasers of the Common Stock for whom the  broker-dealers  may act
as agent or to whom they may sell as  principal,  or from both.  The Company has
paid  or  will  pay  all  expenses  in  connection   with  the  preparation  and
reproduction of the Registration  Statements of which this Prospectus is a part,
which current  expenses are  estimated,  in the aggregate,  to be  approximately
$20,000.  The Company  will not receive any part of the proceeds of any sales by
Selling  Stockholders  of Shares.  However,  the  Company  has  received or will
receive the  exercise  price  payable or paid by Selling  Stockholders  upon the
exercise of Options  issued  under the Plans and upon the  exercise of Warrants.
The Selling  Stockholders will pay the brokerage  commissions charged to sellers
in connection with any sales of Shares thereby hereunder.  In lieu of being sold
pursuant  to this  Prospectus,  any of the Shares  which are  eligible  for sale
pursuant  to Rule 144  under  the  Securities  Act  ("Rule  144") may be sold by
Selling Stockholders under Rule 144. See "Plan of Distribution."

      The Company's  Common Stock trades on the NASDAQ National Market under the
ticker  symbol  "IMCL".  On September  29,  1998,  the closing sale price of the
Common Stock on the NASDAQ National Market was $9 1/16 per share.

      See "RISK FACTORS" beginning on page 7 for a discussion of certain factors
that should be considered  in connection  with an investment in the Common Stock
offered hereby.

      THESE  SECURITIES  HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES
AND  EXCHANGE  COMMISSION  OR ANY  STATE  SECURITIES  COMMISSION,  NOR  HAS  THE
SECURITIES AND EXCHANGE  COMMISSION OR ANY STATE  SECURITIES  COMMISSION  PASSED
UPON THE  ACCURACY OF ADEQUACY OF THIS  PROSPECTUS.  ANY  REPRESENTATION  TO THE
CONTRARY IS A CRIMINAL OFFENSE.

      No dealer,  salesman or any other person has been  authorized  to give any
information or to make any  representations,  other than as contained herein, in
connection  with the  offer  made in this  Prospectus,  and any  information  or
representations  not  contained  herein  must not be relied  upon as having been
authorized by the Company or the Selling Stockholders.  This Prospectus does not
constitute  an offer to sell or a  solicitation  of an offer to buy any security
other than the Common Stock offered by this  Prospectus,  nor does it constitute
an offer to sell or a solicitation of an offer to buy any shares of Common Stock
offered  hereby to any person in any  jurisdiction  where it is unlawful to make
such an offer or  solicitation  to such  person.  Neither  the  delivery of this
Prospectus  nor any sale  hereunder  shall  under any  circumstances  create any
implication  that  information  contained  herein  is  correct  as of  any  time
subsequent to the date hereof.

               The date of this Prospectus is September 30, 1998.
SECTION 10(a) PROSPECTUS; REOFFER
                     PROSPECTUS; POST-EFFECTIVE AMENDMENT TO
                    PREVIOUSLY FILED REGISTRATION STATEMENTS

      Section  10(a)  Prospectus.   The  documents  containing  the  information
specified in Part I of this  Registration  Statement on Form S-8 will be sent or
given to  participants  in the Plans as  specified by Rule  428(b)(i)  under the
Securities  Act of 1933, as amended.  Such documents are not required to be, and
are not being, filed by the Company with the Securities and Exchange Commission,
either as part of this  Registration  Statement or as prospectuses or prospectus
supplements  pursuant to Rule 424 under the  Securities Act of 1933, as amended.
Such documents,  together with the documents  incorporated  by reference  herein
pursuant  to  Item 3 of  Part II of this  Registration  Statement  on Form  S-8,
constitute  a prospectus  that meets the  requirements  of Section  10(a) of the
Securities Act of 1933, as amended.

      Reoffer Prospectus. The material which follows up to but not including the
page beginning Part II of this  Registration  Statement,  constitutes a "reoffer
prospectus," prepared in accordance with the requirements of Part I of Form S-3,
in accordance  with General  Instruction C of Form S-8, to be used in connection
with  reoffers  and resales of  securities  acquired  under the ImClone  Systems
Incorporated  1996 Incentive  Stock Option Plan, As Amended,  and/or the ImClone
Systems Incorporated 1996 Non-Qualified Stock Option Plan, As Amended and/or the
ImClone Systems  Incorporated  1986  Non-Qualified  Stock Option Plan and/or the
ImClone Systems 1986 Incentive  Stock Option Plan and/or under certain  warrants
to acquire shares of Common Stock of the Registrant.

      Post-Effective  Amendment to  Previously  Filed  Registration  Statements.
Pursuant to Rule 429 under the Securities Act of 1933, as amended,  the "reoffer
prospectus"  included as part of this  Registration  Statement  on Form S-8 also
relates to certain  securities  registered under ImClone Systems  Incorporated's
Registration Statement on Form S-8 (File No. 33-95894) filed with the Securities
and Exchange  Commission  and declared  effective on August 24, 1995 and ImClone
Systems  Incorporated's  Registration Statement on Form S-8 (File No. 333-10275)
filed with the  Securities  and Exchange  Commission  and declared  effective on
August 15, 1996 (together, the "Prior Registration Statements"), is intended for
use therewith and  constitutes a  post-effective  amendment to each of the Prior
Registration  Statements.   Such  "reoffer  prospectus"  is  being  filed  as  a
post-effective  amendment  to  each  of the  Prior  Registration  Statements  in
reliance  upon  Item  3(a) of  General  Instruction  C of  Form  S-8  under  the
Securities Act of 1933, as amended.

                                       -i-
TABLE OF CONTENTS

                                                                           Page

AVAILABLE INFORMATION.......................................................1
INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE.............................1
CERTAIN FACTORS AFFECTING FORWARD LOOKING STATEMENTS........................2
PROSPECTUS SUMMARY..........................................................2
RISK FACTORS................................................................7
USE OF PROCEEDS............................................................13
SELLING STOCKHOLDERS.......................................................14
PLAN OF DISTRIBUTION.......................................................16
LEGAL MATTERS..............................................................16
DISCLOSURE OF COMMISSION POSITION ON 
INDEMNIFICATION FOR SECURITIES ACT LIABILITIES.............................17

                                      -ii-
AVAILABLE INFORMATION

      The Company has filed three separate  Registration  Statements on Form S-8
(the "Registration Statements") under the Securities Act with the Commission (as
defined),  with  respect to the shares of Common  Stock of the  Company  offered
hereby.  As  permitted  by the rules and  regulations  of the  Commission,  this
Prospectus omits certain  information  contained in the Registration  Statements
and the exhibits and schedules thereto.  For further information with respect to
the Company and the Common Stock offered  hereby,  the Company is subject to the
informational  requirements  of the Securities  Exchange Act of 1934, as amended
(the  "Exchange  Act"),  and  in  accordance  therewith  files  reports,   proxy
statements  and  other  information  with  the  U.S.   Securities  and  Exchange
Commission  (the  "Commission").   Such  reports,  proxy  statements  and  other
information filed by the Company with the Commission can be inspected and copied
at the Public  Reference Room  maintained by the Commission at 450 Fifth Street,
N.W., Room 1024,  Washington,  D.C.,  20549,  and at the regional offices of the
Commission at 7 World Trade Center,  13th Floor,  New York, New York,  10048 and
Northwestern  Atrium  Center,  500 West  Madison  Street,  Room  1400,  Chicago,
Illinois  60661-2511.  Copies of such  material can be obtained  from the Public
Reference Room of the Commission at 450 Fifth Street, N.W., Washington, D.C., at
prescribed  rates.  Information  regarding the operation of the Public Reference
Room may be obtained by calling the Commission at 1-800-SEC-0330. The Commission
maintains a World Wide Web site that  contains  reports,  proxy and  information
statements and other information  regarding registrants that file electronically
with  the  Commission.  The  address  of that  site is  http://www.sec.gov.  The
Company's  Common Stock is traded on the NASDAQ National Market under the ticker
symbol  "IMCL."  Reports,  proxy  statements and other  information  may also be
inspected at the NASDAQ National Market offices located at 1735 K Street,  N.W.,
Washington, D.C. 20006.

      Statements contained in this Prospectus as to the contents of any contract
or other document referred to are not necessarily complete, and in each instance
reference  is made to the copy of such  contract or other  document  filed as an
Exhibit to the  applicable  Registration  Statement or otherwise  filed with the
Commission,  each  such  statement  being  qualified  in all  respects  by  such
reference,  and each  such  contract  or other  document  shall be  deemed to be
incorporated by reference into this Prospectus.

                 INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

      The following documents, including all amendments filed for the purpose of
completing  or updating such reports,  which have been  heretofore  filed by the
Company with the Commission pursuant to the Exchange Act are hereby incorporated
by reference and made a part hereof:

      1.    The  Company's  Annual Report on Form 10-K for the fiscal year ended
            December 31, 1997.

      2.    The Company's Quarterly Reports on Form 10-Q for the fiscal quarters
            ended March 31, 1998 and June 30, 1998.

      3.    The Company's  Current  Report on Form 8-K, dated February 10, 1998.
            
      4.    The description of the Company's  Common Stock,  par value $.001 per
            share,contained  in its  registration  statement  on Form 8-A  filed
            under the Exchange Act,  including any amendment or report filed for
            the purpose of updating such description.

      All other documents  filed by the Company with the Commission  pursuant to
Sections  13(a),  13(c), 14 and 15(d) of the Exchange Act subsequent to the date
of this Prospectus and prior to the filing of a post-effective  amendment to the
applicable  Registration  Statement which indicates that all securities  offered
have been sold or which de-registers all securities then remaining unsold, shall
be deemed to be  incorporated  by reference in this  Prospectus and to be a part
hereof  from the date of  filing  of such  documents  (such  documents,  and the
documents  enumerated above,  being hereinafter  referred to collectively as the
"Incorporated Documents").

         Any statement contained in an Incorporated  Document shall be deemed to
be modified or superseded  for purposes of this  Prospectus to the extent that a
statement  contained  therein or in any other  subsequently  filed  Incorporated
Document modifies or supersedes such statement.  Any such statements so modified
or  superseded  shall not be deemed,  except as so  modified or  superseded,  to
constitute a part of this Prospectus.

                                       1
The Company undertakes to provide without charge to each person (including
any beneficial owner) to whom a copy of this Prospectus is delivered,  upon oral
or written request of such person, a copy of any and all of the information that
has been or may be  incorporated  by  reference in this  Prospectus,  other than
exhibits to such  documents.  Requests for such copies should be directed to the
attention of John B. Landes,  Vice President,  Business  Development and General
Counsel,  ImClone Systems Incorporated,  180 Varick Street, 7th Floor, New York,
New York 10014; (212) 645-1405.

              CERTAIN FACTORS AFFECTING FORWARD LOOKING STATEMENTS

      This  Prospectus,  including the documents  and  information  incorporated
herein by reference,  contains forward-looking  statements within the meaning of
Section 27A of the  Securities  Act that  involve  risks and  uncertainties.  In
connection with the safe harbor provisions of the Private Securities  Litigation
Reform  Act of 1995,  the  Company  is hereby  providing  cautionary  statements
identifying  important  factors that could cause the Company's actual results to
differ  materially  from those expressed in  forward-looking  statements made in
this Prospectus,  including the documents and information incorporated herein by
reference. Any statements that express beliefs, plans,  objectives,  assumptions
or future events or performance (often, but not always, through the use of words
of phrases such as "will likely result," "are expected to," "will continue," "is
anticipated,"  "estimate,"  "intends," "plans," "projection," and "outlook") may
be  forward-looking  and,  accordingly,  such statements may involve  estimates,
assumptions,  risks and  uncertainties  which  could  cause  actual  results and
performance  of the Company to differ  materially  from those  expressed  in the
forward-looking  statements.  In  evaluating  the  Company  and its  operations,
performance and results,  investors should consider, among other things, and any
forward-looking  statements  contained in this Prospectus are qualified in their
entirety by reference to, the factors  discussed  herein under the caption "Risk
Factors" and the estimates,  assumptions,  risks and uncertainties  discussed in
the  Company's  most  recent  Annual  Report  on Form 10-K  under  the  captions
"Business" and "Management's  Discussion and Analysis of Financial Condition and
Results of Operations," in the Company's  Quarterly Reports on Form 10-Q, and in
the  Company's  other  reports  filed  under  the  Exchange  Act,  in each  case
incorporated by reference herein.

      The risk factors  described  herein could cause actual results or outcomes
to differ materially from those expressed in any  forward-looking  statements of
the Company or made by or on behalf of the Company,  and  investors,  therefore,
should not place undue reliance on any such forward-looking statements. Further,
any forward-looking statement speaks only as of the date on which such statement
is made, and the Company undertakes no obligation to update any  forward-looking
statement or statements  to reflect  events or  circumstances  after the date on
which such  statement  is made or to reflect  the  occurrence  of  unanticipated
events.  New  factors  emerge  from  time to time,  and it is not  possible  for
management  of the Company to predict all of such factors.  Further,  management
cannot  necessarily  assess  the  impact  of each such  factor on the  Company's
business or the extent to which any factor, or combination of factors, may cause
actual results to differ materially from those contained in any  forward-looking
statements.

                               PROSPECTUS SUMMARY

      The  following  summary is qualified in its entirety by the more  detailed
information,  "Risk  Factors"  and  financial  statements,  including  the notes
thereto,  included  or  incorporated  by  reference  in  this  Prospectus.   The
securities offered hereby involve a high degree of risk. See "Risk Factors."

      General.

      The Company is a  biopharmaceutical  company engaged primarily in research
and  development  of  therapeutic  products  for the  treatment  of  cancer  and
cancer-related    disorders.    The   Company's   product   candidates   include
interventional therapeutics for cancer and cancer vaccines.

      Development Programs.

      C225 Cancer Therapeutic. The Company's lead interventional therapeutic for
cancer is a chimerized (part mouse,  part human) antibody that acts to block the
Epidermal  Growth  Factor  receptor   ("EGFr").   EGFr  has  been  shown  to  be
over-expressed in the cells of approximately  one-third of all solid cancers. It
is also  expressed in select normal  tissue.  In vivo animal  studies with human
tumors have shown that C225 in combination with various  chemotherapeutic agents
(doxorubicin,  cisplatin or paclitaxel) demonstrates a pronounced enhancement of
the  anti-tumor  effect  of  the  chemotherapeutic   agents,  resulting  in  the
elimination  of human  tumors  established  in these  animals.  The studies have
demonstrated  long-term  tumor-free survival 

 
                                      2
of  animals.  The  Company's  research  has also  shown that C225 used alone has
efficacy in renal cell carcinoma and pancreatic carcinoma animal models.

      Since  December  1994,  the Company has  initiated  several  Phase  Ib/IIa
clinical  trials of C225 at Memorial  Hospital (the patient care arm of Memorial
Sloan-Kettering   Cancer  Center)   ("Sloan-Kettering"),   Yale  Cancer  Center,
University of Virginia, MD Anderson Cancer Center and the University of Alabama,
among  others.  These  studies  have  involved  intravenous   administration  of
escalating  doses of C225,  both with and without  chemotherapeutic  agents,  in
patients with various solid cancers. Several of these studies are ongoing. These
studies  have  shown that the drug is  generally  well-tolerated.  In 1997,  the
Company  initiated  Phase Ib/IIa studies in head and neck cancer  patients using
C225 alone (begun in July 1997), in conjunction  with cisplatin  (begun in April
1997) and in conjunction with radiation (begun in April 1997). Additionally,  in
December  1997,  the  Company  initiated  a  multi-center,  open label  Phase II
clinical  trial to evaluate the effect of C225 on time to progression of disease
in 53 patients with  metastatic  renal cell  carcinoma.  The Company  expects to
initiate  Phase  II/III  studies to evaluate  the  potential  of C225 in various
additional tumor types, such as head and neck and pancreatic cancers.

      BEC2 Cancer Vaccine.  BEC2 is a monoclonal  anti-idiotypic  antibody which
the Company  believes  may be useful to prevent or delay the onset of  recurrent
primary tumors or metastatic disease. The antibody, which mimics the ganglioside
GD3,  has been tested since 1991 in Phase I clinical  trials at  Sloan-Kettering
against  certain  forms of  cancer,  including  small  cell lung  carcinoma  and
melanoma.  There has been evidence of prolonged  survival of patients with small
cell lung  carcinoma in a pilot study  involving  BEC2 at  Sloan-Kettering.  The
Company has granted  Merck KGaA,  formerly E. Merck  ("Merck"),  a  German-based
pharmaceutical  company,   exclusive  rights  to  manufacture  and  market  BEC2
worldwide,  except  that in North  America,  Merck  does  not have the  right to
manufacture  BEC2 and the Company has retained the right to co-promote  BEC2. It
is the  intent  of the  parties  that  the  Company  will  be the  bulk  product
manufacturer of BEC2 to support worldwide sales. In return,  Merck is paying the
Company  research  support,  is required to pay the Company  milestone  fees and
royalties  on future  sales,  if any,  and will share with the Company  revenues
associated  with  the  sale of BEC2 by  Merck  in  North  America.  A Phase  III
multinational clinical trial for BEC2 in treatment of limited disease small cell
lung carcinoma has been opened and patient enrollment has been initiated.

      Chimerized Monoclonal Antibody Inhibitor of Angiogenesis.  The Company has
developed a monoclonal antibody, c-p1C11, which is specific for the KDR receptor
for Vascular  Endothelial  Growth Factor ("VEGF").  The antibody is currently in
pre-clinical  studies in preparation  for the filing of an  Investigational  New
Drug ("IND")  Application  and the further testing of the product as a potential
cancer  therapeutic.  The  Company is also  preparing  a  humanized  form of the
antibody,  in conjunction with MRC Collaborative  Center. KDR and VEGF are known
to be involved in  angiogenesis,  which is the natural  process of growth of new
blood vessels. A therapeutic product that would inhibit angiogenesis could be of
value in treatment of cancer as well as other  diseases that depend on growth of
blood vessels, such as diabetic retinopathy, macular degeneration and rheumatoid
arthritis.

      Research Programs.

      In addition to concentrating on its products in clinical development,  the
Company performs ongoing research in a number of related areas.

      Interventional Therapeutics. The Company conducts an interventional cancer
therapeutic research program in the development of inhibitors of tyrosine kinase
receptors (growth factor receptors)  associated with tumor cell regeneration and
support.

      In addition to its  chimerized  monoclonal  antibody in  development,  the
Company is seeking to develop other  antibodies  that inhibit  angiogenesis.  In
connection  with this research and  development of the  chimerized  angiogenesis
inhibitor,  the Company is  sponsoring  research  programs  at various  academic
institutions to test KDR specific therapeutics in animal models.

      The  Company  has also  initiated  a program  to  develop  small  molecule
antagonists of growth factor receptors,  including both angiogenic growth factor
receptors  and EGF  receptors.  In October  1997,  the Company  entered  into an
agreement with CombiChem, Inc. ("CombiChem"), a combinational chemistry company,
pursuant  to which the  Company  has  access  to  CombiChem's  library  of small
molecules  for  screening in the  Company's  assays for  identification  of lead
candidates. The Company also made an equity investment in CombiChem. The Company
has also entered into an agreement with the Institute for Molecular  Medicine in
Freiburg,  Germany to screen small molecule  therapeutic  candidates,  including
those provided by the compound libraries of CombiChem,  against various tyrosine
receptors.

                                       3
The Company is conducting research on the validation of  vascular-specific
cadherin   ("VE-cadherin")   as  a  novel   potential  drug  target  to  inhibit
cancer-associated  angiogenesis.  VE-cadherin  is believed to play an  important
role in angiogenesis by enabling the assembly of endothelial cells into vascular
tubes.  Cancer growth is dependent on the formation of a capillary  blood vessel
network in the  tumor,  and  VE-cadherin  antagonists  may thus have  utility as
anti-cancer  agents.  The  Company  will  test  monoclonal   antibodies  against
VE-cadherin as potential  angiogenesis  inhibitors  and use its  high-throughput
assays for the  identification  of small  molecule  VE-cadherin  inhibitors.  In
connection with this program,  the Company has also acquired exclusive rights to
VE-cadherin-2   and  to   antibodies  to   VE-cadherin,   and  has  initiated  a
collaboration  with Mario Negri Institute for  Pharmacological  Research (Milan,
Italy)  to  conduct  pharmacological  research  in the role of  VE-cadherins  in
antiogenesis.

      Cancer Vaccines.  The Company seeks to discover  potential cancer vaccines
as another route to cancer  treatment.  Cancer  vaccines would  activate  immune
responses to tumors to protect  against  local  spread,  distant  metasteses  or
recurrence of cancer.  Choosing  appropriate  cancer cell targets and generating
effective  immune  responses  are the  focus  of the  Company's  cancer  vaccine
program.  For  example,  research  is being  conducted  on a possible  malignant
melanoma vaccine based on the tumor associated  antigen known as gp75.  Patients
with  malignant  melanoma  are  known to  produce  antibodies  and T cells  that
recognize  gp75.  Animal studies have shown that a gp75 cancer vaccine is highly
effective in eliciting an immune response  against melanoma cells and preventing
or inhibiting growth of experimental melanoma tumors in mice.

      Endothelial Stem Cell Technology.  The Company has proprietary  technology
capable of isolating endothelial stem cells and is exploring uses of endothelial
stem cells for stimulation of collateral  blood  circulation in ischemias (e.g.,
myocardial ischemia and peripheral vascular disease) as well as for gene therapy
delivery. The Company is considering whether to pursue this research directly or
through   its   recently   established   wholly-owned   subsidiary,    EndoClone
Incorporated.

      Hematopoiesis. The Company is conducting research in hematopoiesis (growth
and development of blood cell elements) aimed at discovering  factors to support
hematopoietic stem cells and to control the proliferation,  differentiation  and
functional deterioration of hematopoietic elements.

      The Company has an  exclusive  license  from The  National  Institutes  of
Health ("NIH") to the delta-like  ("DLK")  protein and gene for use in stem cell
and gene therapy.  DLK is a member of a family of proteins  which appear to have
the ability to maintain cells in an undifferentiated state.

      The  Company  also has  entered  into a  non-exclusive  license and supply
agreement with Immunex Corporation ("Immunex") for use of the FLK-2/FLT-3 ligand
for ex vivo cell therapies.  Immunex has taken a license from the Company to the
FLK-2  receptor,  the scope of which is  limited  to the use by  Immunex  in the
manufacture of the FLK-2/FLT-3  ligand.  Immunex is currently testing the ligand
in human trials for stem cell mobilization and for tumor inhibition.

      The Company also has rights to  recombinant  mutein form of  Interleukin-6
("interleukin-6m"  or  "IL-6m")  which it has  tested in human  trials in cancer
patients to seek to  stimulate  platelet  production.  The Company is  currently
monitoring third party research with IL-6m to explore the possibility that IL-6m
may be a critical factor in liver cell regeneration.

      Licensed Diagnostics and Infectious Disease Vaccines.

      The Company has licensed its  diagnostic and  infectious  disease  vaccine
product areas, based on its earlier research,  to corporate partners for further
development  and  commercialization.  The Company has granted the  Wyeth/Lederle
vaccine and pediatrics division of American Home Products Corporation ("American
Home") a worldwide  license to  manufacture  and market its  infectious  disease
vaccines, which are in development. In January 1998, this agreement was extended
to allow the  continuation  through  September 1999 of pre-clinical  research in
preparation for clinical trials of infectious disease candidate vaccines for the
treatment  of  gonorrhea  and the receipt by the Company of annual  funding from
American Home during such period in the amount of $300,000. The Company has also
entered into a strategic alliance with Abbott  Laboratories  ("Abbott") pursuant
to which the Company has licensed  certain of its diagnostic  products to Abbott
on a worldwide basis. In mid-1995, Abbott launched in Europe its first DNA-based
test,  using the Company's  proprietary  Repair Chain Reaction ("RCR") DNA probe
technology,  for the diagnosis of the sexually  transmitted  disease  chlamydia.
Abbott has added tests for gonorrhea and mycobacteria, and has launched sales in
the United States as well.  In December  1996,  the Company and Abbott  modified
this  agreement to provide for an exclusive  sublicensing  agreement with Chiron
Diagnostics  ("Chiron")  for the  Company's  patented  DNA signal  amplification
technology,  AMPLIPROBE.  Under the terms of the  agreement  all sales of Chiron
branched DNA diagnostic probe technology in countries covered by Company patents
will be subject to a royalty to Abbott to be passed through to the Company.

                                       4
Research and Development.

      The Company  initiated its in-house  research and development in 1986. The
Company has assembled a scientific staff with a variety of complementary  skills
in  a  broad  base  of  advanced  research  technologies,   including  oncology,
immunology,  molecular  and cell  biology,  antibody  engineering,  protein  and
synthetic  chemistry  and  high-throughput   screening.  The  Company  has  also
recruited  a  staff  of  technical  and  professional  employees  to  carry  out
manufacturing  of  clinical  trial  materials  at  its  Somerville,  New  Jersey
manufacturing  facility.  In addition to its research programs pursued in-house,
the Company collaborates with certain academic  institutions and corporations to
support  research in areas of the Company's  product  development  efforts.  The
Company has also entered into collaborations with major pharmaceutical companies
in order  to  obtain  funding  and  product  development  and  commercialization
assistance  for certain of its  therapeutic  product  candidates in exchange for
specific product licensing rights.  The Company intends to enter into additional
agreements of this nature with appropriate  pharmaceutical company partners with
the resources and experience to assist the Company  financially to  successfully
bring its products to market, both in the United States and abroad. There can be
no assurance,  however,  that the Company will be successful in consummating any
such arrangements.

      In addition to its research programs pursued in-house and in collaboration
with  corporate  partners,   the  Company  collaborates  with  certain  academic
institutions  to support  research  in areas  related to the  Company's  product
development  efforts.  These institutions  include,  but are not limited to, the
National  Cancer  Institute,  Sloan-Kettering,  the  University  of  California,
Princeton  University,  the University of North Carolina,  The Wistar Institute,
The  University  of  Texas  Southwestern  Medical  Center  and The  Mario  Negri
Institute for Pharmacological  Research.  Usually, research supported at outside
academic  institutions  is performed in  conjunction  with  additional  in-house
research.  The Company also has collaborations with institutions  related to the
performance  of its clinical  trials.  Such  institutions  include,  but are not
limited to, Sloan-Kettering,  Yale Cancer Center, the University of Virginia, MD
Anderson Cancer Center, and the University of Alabama.

      The  Company  operates  a  facility  in  Somerville,  New  Jersey  for the
manufacture  of bulk  materials  of its  therapeutic  candidates  in quality and
quantity sufficient for human clinical trials. At this facility,  the Company is
producing C225 bulk drug. At this facility,  the Company also supports  clinical
development of both the C225 and BEC2 programs.

      The  Company  was  incorporated  in  Delaware  in 1984 and  commenced  its
principal  research and  development  operations  in March 1986.  The  Company's
principal  executive  offices and laboratories are located at 180 Varick Street,
New York, New York, 10014, and the telephone number is (212) 645-1405.

      The Offering.

Common Stock being Offered ............      The   Prospectus   relates   to  an
                                             offering     by     the     Selling
                                             Stockholders  of  up  to  2,852,874
                                             shares of Common Stock which may be
                                             acquired,  or have been acquired by
                                             such Selling  Stockholders upon the
                                             exercise  of  Options  issued as of
                                             the  date  of  this  Prospectus  or
                                             thereafter under the Plans and upon
                                             the exercise of the Warrants.

Common Stock Outstanding
   after the Offering .................      As  of   September   25,  1998  the
                                             Company  had  24,437,522  shares of
                                             Common Stock outstanding.  Assuming
                                             that   all  of  the   Options   and
                                             Warrants     held    by     Selling
                                             Stockholders as of the date of this
                                             Prospectus  are  exercised  and  no
                                             other  shares of  Common  Stock are
                                             issued  following  the date of this
                                             Prospectus,  the Company would have
                                             26,833,901 shares of  Common  Stock
                                             outstanding.

Use of Proceeds .......................      The  Company  will not  receive any
                                             proceeds   from  the  sale  of  the
                                             Shares   offered  by  the   Selling
                                             Stockholders.  However, the Company
                                             has  received  or will  receive the
                                             exercise  price  payable or paid by
                                             Selling   Stockholders   upon   the
                                             exercise  of Options  issued  under
                                             the Plans and upon the  exercise of
                                             Warrants. If all of the Options and
                                             Warrants   held   by  the   Selling
                                             Stockholders as of the date of this
                                             Prospectus   are   exercised,   the
                                             Company  will   receive   aggregate
                                             estimated  proceeds  in  connection
                                             with the  payment  of the  exercise
                                             prices of such Options and Warrants
                                             (including any amounts 
 

                                       5
received in respect  thereof by the
                                             Company  in  connection   with  the
                                             exercise  of Options  and  Warrants
                                             prior   to   the   date   of   this
                                             Prospectus)    of     approximately
                                             $17,562,000.       The      Company
                                             anticipates   using  any   proceeds
                                             received,  and has  used  any  such
                                             proceeds previously received,  upon
                                             the  exercise  of the  Options  and
                                             Warrants  (i) to  continue  to fund
                                             and   expand   its   research   and
                                             development  programs  and (ii) for
                                             general     corporate     purposes,
                                             including working capital. See "Use
                                             of Proceeds." 
NASDAQ National
  Market Symbol........................      IMCL

Risk Factors...........................      See "Risk Factors" for a discussion
                                             of certain risk factors that should
                                             be   considered   by    prospective
                                             investors  in  connection  with  an
                                             investment  in the  Shares  offered
                                             hereby.

                                       6
RISK FACTORS

      An investment  in the Shares  offered by this  Prospectus  involves a high
degree of risk. In addition to the other  information  contained or incorporated
by reference in this  Prospectus,  the  following  factors  should be considered
carefully in evaluating an investment in the Shares offered hereby.

      Early Stage of Product Development; Technological Uncertainty.

      The Company was founded in 1984 and opened its  laboratory  in New York in
1986.  Substantially all of the Company's  products are in research or the early
stages of development or clinical  studies.  Substantially  all of the Company's
revenues were  generated from license and research  arrangements  with corporate
sponsors.  The Company's revenues under its research and license agreements with
corporate  sponsors have fluctuated and are expected to fluctuate  significantly
from period to period.  Similarly,  the  Company's  results of  operations  have
fluctuated  and are expected to fluctuate  significantly  from period to period.
These  variations  have been,  and are  expected to be,  based  primarily on the
timing of entering into supported research and license agreements, the status of
development of the Company's various products,  the timing and level of revenues
from sales by its  partner in  diagnostics,  Abbott,  of  products  bearing  the
Company's  technology,  the  addition or  termination  of  research  programs or
funding support,  performance by the Company's corporate  collaborators of their
funding obligations,  the achievement of specified research or commercialization
milestones  and  variations  in the  level  of  expenditures  for the  Company's
proprietary  products  during any given  period.  The  Company's  products  will
require substantial  additional  development and clinical testing and investment
prior to commercialization. To achieve profitable operations, the Company, alone
or with others, must successfully develop, introduce and market its products. No
assurance can be given that any of the  Company's  product  development  efforts
will be  successfully  completed,  that  required  regulatory  approvals  can be
obtained or that any products, if developed,  will be successfully  manufactured
or marketed or achieve customer acceptance.

      History of Operating Losses and Accumulated Deficit.

      The  Company has  experienced  significant  operating  losses in each year
since its  inception,  due  primarily to  substantial  research and  development
expenditures.  As of June 30, 1998,  the Company had an  accumulated  deficit of
approximately $125 million. The Company expects to incur significant  additional
operating losses over each of the next several years.

      Cash Requirements; Need for Additional Funding.

      The  Company  has  expended  and will  continue  to expend  in the  future
substantial  funds to continue  the research and  development  of its  products,
conduct   preclinical  and  clinical  trials,   establish   clinical-scale   and
commercial-scale  manufacturing  in its own  facilities or in the  facilities of
others, and market its products.

      The Company  expects to incur  substantial  funding  requirements  for the
expansion of operations,  including (i) the expansion of the clinical  trials of
C225 and the related  manufacturing  program to support  these  trials which may
include  expansion of the Company's  facilities and (ii) in an effort to develop
new product  candidates,  the expansion of research and  development  activities
including among other things,  increased staffing, the acquisition of equipment,
and the consummation of new outside research agreements. In addition, $2,200,000
of the Industrial  Development  Revenue Bonds issued by the New York  Industrial
Development  Agency  ("NYIDA") in 1990 with a scheduled  maturity in 2004 become
due upon the earlier  termination  of the lease (the  "Lease") for the Company's
New York facility.  The Lease is scheduled to expire in March 1999, however, the
Company  currently  expects  to be able to extend  the Lease  and  retrofit  the
facility to better suit its needs,  although  there is no assurance that it will
be able to do so. Assuming the extension of the Lease,  the Company expects that
the ongoing research support of its corporate partners,  together with its other
capital  resources,  will be  sufficient  to enable it to fund its  current  and
planned  operations  through the end of the year 2000. The receipt of certain of
such ongoing  research  support is subject to the  attainment  by the Company of
specified  research and  development  milestones,  certain of which have not yet
been  achieved.  No  assurance  can be given  that there will not be a change in
projected research support (including research and development  milestones),  or
in other  expenses that would lead to the Company's  capital being consumed at a
faster rate than  currently  expected,  or that the Lease will be extended.  The
Company will require  significant  levels of  additional  capital and intends to
raise the necessary  capital  through  additional  arrangements  with  corporate
partners, equity or debt financings or from other sources. There is no assurance
that the Company will be successful in  consummating  any such  arrangements  or
financings.  If adequate funds are not available, the Company may be required to
significantly curtail its planned operations.

                                       7
The Company has entered into  preliminary  discussions  with several major
pharmaceutical  companies concerning the funding of research and development for
certain of its products in research.  No assurance can be given that the Company
will be successful in pursuing any such alternatives.  In addition,  the Company
is in preliminary  discussions with several major pharmaceutical  companies with
respect  to a  strategic  alliance  for  the  development  of its  lead  product
candidate,  C225.  Such a strategic  alliance  could include an up-front  equity
investment  by such a company  in the  Company,  as well as the  payment  to the
Company of technology access fees, milestone fees and revenue sharing. There can
be no  assurance  that the  Company  will be  successful  in  achieving  such an
alliance,  nor can the  Company  predict  the  amount  of funds  which  might be
available  to it if it entered  into such an  alliance or the time at which such
funds would be made available.

      Pursuant  to the terms of the  Company's  Series A  Convertible  Preferred
Stock (the  "Series A  Preferred  Stock" or "Series A  Preferred  Shares"),  the
holders of the Series A Preferred  Shares are entitled to receive,  out of funds
legally available therefor, cumulative dividends at the annual rate of $6.00 per
share, compounded annually. Dividends are payable on the then outstanding Series
A Preferred  Shares in cash upon the earlier of (i) annually on December 31st of
each year  beginning on December 31, 1999;  or (ii) at the time of conversion or
redemption of the Series A Preferred Shares on which the dividend is being paid.
Dividends on the Series A Preferred  Shares  accumulate and accrue from December
15, 1997 (the date of original issuance) and accrue  thereafter,  whether or not
earned or declared.  As of June 30, 1998,  dividends  aggregating  approximately
$1,302,000 had accrued on the Series A Preferred Shares.

      Dilution.

      Warrants to purchase 2,281,050 shares of the Company's Common Stock (which
includes  1,314,850  warrants  held  by  directors,   officers,   employees  and
consultants of the Company), at an average exercise price of approximately $2.79
per share (subject to adjustment) and stock options to purchase 4,548,424 shares
of the  Company's  Common Stock (which  includes  4,098,424  options  granted to
directors,  officers,  employees  and  consultants  of  the  Company  under  the
Company's stock option plans at an average exercise price of approximately $7.90
per share (subject to  adjustment),  were  outstanding as of September 25, 1998.
The shares  underlying  such  options and  warrants  (including  the Options and
Warrants which are covered by this  Prospectus) are covered,  or will be covered
prior  to  exercise,  by  effective  registration  statements  on file  with the
Commission.  For the life of such options and warrants,  the holders thereof are
given an  opportunity  to benefit  from a rise in the market price of the Common
Stock with a resulting  dilution  of the  interest  of other  stockholders.  The
exercise of such options and warrants is likely to be  undertaken at a time when
the Company, in all probability, could obtain additional equity capital from the
public on terms more  favorable  than those provided for pursuant to the options
and warrants.  The exercise of a  significant  number of options and warrants at
any one time or the sale of a  substantial  number of  shares  of  Common  Stock
acquired upon exercise of options or warrants could adversely  affect the market
price  of the  Company's  Common  Stock  and  the  Company's  ability  to  raise
additional equity capital.

      As  of  September  25,  1998,  400,000  Series  A  Preferred  Shares  were
outstanding.  The Series A Preferred Shares have a stated value of $100. 100,000
Series A Preferred  Shares were  immediately  convertible  into Common  Stock on
December  15,  1997  (the  "Issuance  Date");  an  additional  100,000  Series A
Preferred  Shares  become  convertible  on or after January 1, 2000 (the "Second
Anniversary  Date");  an  additional  100,000  Series A Preferred  Shares become
convertible on or after January 1, 2001 (the "Third  Anniversary  Date"); and an
additional  100,000  Series A Preferred  Shares become  convertible  on or after
January 1, 2002 (the  "Fourth  Anniversary  Date").  Series A  Preferred  Shares
converted on or after the Issuance  Date and before the Second  Anniversary  are
convertible at a per share conversion price of $12.50; Series A Preferred Shares
converted  on or  after  the  Second  Anniversary  Date  and  before  the  Third
Anniversary  Date are convertible at a per share  conversion  price equal to the
Average  Market Price of the Common Stock for the five (5)  consecutive  trading
days  ending one  trading  day prior to the Second  Anniversary  Date;  Series A
Preferred Shares converted on or after the Third Anniversary Date and before the
Fourth Anniversary Date are convertible at a per share conversion price equal to
the  Average  Market  Price of the  Common  Stock  for the five (5)  consecutive
trading days ending one trading day prior to the Third  Anniversary Date; Series
A Preferred Shares converted on or after the Fourth  Anniversary Date and before
January 1, 2003 are convertible at a per share  conversion price equal to 88% of
the  Average  Market  Price of the  Common  Stock  for the five (5)  consecutive
trading days ending one trading day prior to the Fourth  Anniversary  Date;  and
Series A Preferred  Shares converted on or after January 1, 2003 are convertible
at a per share  conversion price equal to the Average Market Price of the Common
Stock for the five (5) consecutive  trading days ending one trading day prior to
the receipt by the Company of a notice of conversion.  For purposes of computing
the conversion price,  "Average Market Price" of the Common Stock for any period
is the average of the closing  prices for the Common  Stock for each trading day
in such period as reported by the NASDAQ  National  Market or any trading system
on which the Common Stock may then be quoted. The conversion price is subject to
adjustment in the case of certain  

                                       8
dilutive  events.  Further,  in the event the Average Market Price of the Common
Stock for the five (5) consecutive  trading days ending one trading day prior to
any  trading  day during  which any Series A  Preferred  Shares are  outstanding
exceeds 150% of the conversion  price then in effect,  the Company has the right
to  require  the  holder of the Series A  Preferred  Shares to convert  all such
shares as may then be convertible. In connection with the issuance of the Series
A Preferred Shares,  Merck was granted certain  registration rights with respect
to the underlying  shares of Common Stock.  Due to the fact that,  commencing on
the Second  Anniversary  Date,  the number of shares of Common  Stock into which
Series A Preferred  Shares are convertible is not fixed,  and is determined with
reference to the market prices of the Company's Common Stock as described above,
as the market price of the Common Stock decreases, the number of shares issuable
upon conversion of the Series A Preferred Shares will increase.

      Limited Manufacturing Experience.

      To  be  successful,   the  Company's  products  must  be  manufactured  in
commercial  quantities  in  compliance  with  regulatory   requirements  and  at
acceptable costs.  Although the Company has developed products in the laboratory
and  in  some  cases  has  produced  sufficient   quantities  of  materials  for
pre-clinical  animal trials and early stage clinical trials,  production in late
stage clinical or commercial  quantities may create technical challenges for the
Company.  The  Company  owns a  facility  which  is used  as its  clinical-scale
manufacturing facility. If it commercializes its products, the Company may adapt
this facility or outfit an additional  facility for use as its  commercial-scale
manufacturing   facility.   However,  the  Company  has  limited  experience  in
clinical-scale    manufacturing   and   no   experience   in    commercial-scale
manufacturing,  and no  assurance  can be given that the Company will be able to
make the transition to late stage clinical or commercial production.  The timing
and any  additional  costs of adapting the  Company's  facility or outfitting an
additional facility for commercial manufacturing will depend on several factors,
including the progress of products through clinical trials,  and such timing and
additional costs are not yet determinable.

      Establishing Sales and Marketing Capability.

      As  a  research  and  development  company,  the  Company  does  not  have
significant  experience  in selling or marketing  new  products.  The  Company's
current strategy does not necessarily  include marketing products on its own, as
it may do so initially through,  or in conjunction with, its corporate partners.
See "Risk  Factors-Dependence  on Certain Contractual  Agreements with Corporate
Partners.  " At such time as the Company seeks to market directly a new product,
the Company  will  require  expertise  in sales and  marketing.  There can be no
assurance that the Company will be able to retain qualified or experienced sales
and marketing personnel or that any efforts undertaken by such personnel will be
successful.  Under the Company's agreement with Merck, the Company has the right
to  co-market  BEC2 in North  America in the event BEC2 is approved  for sale in
North America.

      Dependence on Certain Contractual Agreements with Corporate Partners.

      To date,  the  Company  has  derived  substantially  all,  and the Company
expects to continue to derive over the next several years a substantial portion,
of its  revenues  related to research  and  development  funding and license fee
revenues from agreements with corporate  partners.  These  agreements  typically
provide the corporate  partner with certain rights to manufacture  and/or market
in certain  geographic  areas  specified  products which are developed using the
Company's proprietary  technology,  subject to an obligation to pay royalties to
the Company based on future product sales, if any.  Certain of these  agreements
provide for funding by corporate  partners of research  activities  performed by
the  Company,  and in some cases for  payments to the  Company of license  fees,
either upon  entering  into such  agreements  or upon  achievement  of specified
research,  regulatory and commercialization  milestones,  or both. The Company's
revenues  from these  agreements  are not  received at regular  intervals,  have
fluctuated in the past, and are expected to continue to fluctuate in the future.
In general,  the  agreements  from which the Company  derives such  revenues are
subject to early  termination at the election of the corporate  partner.  In the
past, some of these  arrangements  have been  terminated.  There is no assurance
that revenues from these  sources will be  maintained,  or that the Company will
enter into any additional agreements of a similar nature.

      Under  most of these  agreements,  the  corporate  partner,  at least  for
certain  territories,  controls and is responsible for the design and conduct of
pre-clinical and clinical trials, seeking and obtaining of regulatory approvals,
establishing  clinical  and  commercial-scale   manufacturing  capabilities  and
manufacturing and marketing of products in those  territories.  Pursuant to such
agreements,  the  amount  and  timing of  funding  and the  investment  of other
resources are  controlled by such other parties 

                                       9
and also are subject to the risk of  financial  or other  difficulties  that may
befall such other  parties.  In addition,  the Company's  corporate  partners or
their affiliates may be pursuing alternative products or technologies addressing
the same purposes as those which are the subject of their collaboration with the
Company.  While the Company believes its corporate partners have or will have an
economic  motivation  to  succeed in  performing  their  obligations  under such
agreements,  there  can  be  no  assurance  that  the  corporate  interests  and
motivations of these partners will remain consistent with those of the Company.

      Uncertainties as to Patents and Proprietary Technologies.

      The patent  position of  biopharmaceutical  companies  generally is highly
uncertain  and  involves  complex  legal and factual  questions.  The  Company's
success  will  depend,  in part,  on its  ability  to obtain  patents on its own
products,  obtain  licenses to use third  parties'  technologies,  protect trade
secrets, and operate without infringing the proprietary rights of others. If the
Company is unable to obtain patents that adequately protect its own products, or
if any of the  Company's  proprietary  technologies  were to  conflict  with the
rights of others,  the Company's  ability to  commercialize  products using such
technologies could be materially and adversely affected.

      The Company  currently is the exclusive  licensee or assignee of 42 issued
patents worldwide,  24 of which are issued United States patents. The Company is
the  assignee  or  exclusive  licensee  of  approximately  36 families of patent
applications  in the  United  States and in foreign  countries  directed  to its
proprietary  technology.  There can be no assurance that patents will issue as a
result of any of such  applications.  Nor can there be any assurance that issued
patents would be of substantial  protection or commercial benefit to the Company
or would afford the Company  adequate  protection from competing  products.  For
example,  issued  patents may be challenged and declared  invalid.  In addition,
under many of its license agreements with third parties, the Company is required
to meet  specified  milestone or diligence  requirements  in order to retain its
license to such third  party  patents and patent  applications.  There can be no
assurance that the Company will satisfy any of these requirements.

      The  Company  holds  rights  under  certain  third party  patents  that it
considers  necessary for the  development of its  technology.  It is anticipated
that,  in order to  commercialize  certain of the  products  that the Company is
developing  or may  develop,  the Company  may be required to obtain  additional
licenses  to  patents  from  third  parties.  However,  the extent to which such
licenses may be required, the availability of such licenses and the cost of such
licenses, if they are available, are uncertain, at present.

      The Company is aware that other parties have filed patent  applications in
various countries in several areas in which the Company is developing  products.
Some of these  patent  applications  have  issued as patents  and some are still
pending. There can be no assurance that the pending patent applications will not
issue as patents.  Issued  patents are entitled to a rebuttable  presumption  of
validity under the laws of the United States and certain other countries.  These
issued  patents  may  adversely  affect the  ability  of the  Company to develop
commercial products it is attempting to develop. If licenses to such patents are
needed,  there can be no assurance that any such licenses would be obtainable by
the Company on acceptable terms.

      The  following are some of the areas in which the Company may be adversely
affected by the patents and patent applications of others:

      The Company  has an  exclusive  license to an issued  U.S.  patent for the
murine form of C225, the Company's EGFr antibody product. The Company's licensor
did not seek patent  protection  outside the United  States with respect to this
antibody.  Outside the United States, the Company is relying, in part, on patent
applications  exclusively  licensed  from a major  pharmaceutical  company which
claim the use of an EGFr antibody in conjunction with  chemotherapeutic  agents.
The  Company  is  currently  prosecuting  these  applications.  There  can be no
assurance that the Company will be successful in these efforts.

      The  EGFr  antibody  being  developed  by the  Company  is a  "chimerized"
monoclonal antibody.  Patents have been issued to other biotechnology  companies
that cover the  chimerization of antibodies,  and the Company may be required to
obtain  licenses  under these patents in order to  commercialize  its chimerized
monoclonal  antibodies.  There can be no assurance that the Company will be able
to obtain such licenses in the territories where it proposes commercialization.

      The  Company is aware that  third-party  patents  have been  issued in the
United States and Europe covering anti-idiotypic antibodies and/or their use for
the treatment of tumors. Such patents, if valid, could be construed to cover the
Company's BEC2 monoclonal antibody and certain uses thereof in the United States
and most of Europe. Merck, the Company's licensee of BEC2 worldwide (except that
the Company has retained the right to co-promote BEC2 in the United States), has
informed the Company that it has obtained a non-exclusive,  worldwide license to
such patent in order to market 

                                       10
BEC2 in its  territory.  No assurance  can be given that such  license  would be
available to the Company in other parts of the world on commercially  acceptable
terms, if at all.

      The   Company   maintains  a   proprietary   position   with   respect  to
anti-angiogenic  therapeutics,  as  well  as  therapeutic  methods  of  treating
angiogenic  disease,  through  patents  and  patent  applications  filed  by the
Company.  The Company is aware that third parties have filed patent applications
that could  affect  the  ability of the  Company  to  commercialize  some of its
anti-angiogenic therapeutics or therapeutic treatments.

      The United Sates Patent and  Trademark  Office has granted two patents for
the Company's  cysteine-depleted IL-6 molecular variant, IL-6m, and the DNA that
encodes IL-6m.  The patent and patent  applications  are co-owned by the Company
and the  University  of North  Carolina,  whose  rights  have  been  exclusively
licensed to the Company. The Company is aware of patents issued to a third party
in  the  United  States  and  Europe  covering  cysteine-depleted  proteins.  In
addition,  the Company is aware of third-party  patents for both recombinant and
native IL-6 and methods for its  production.  The Company is aware of a European
patent for the DNA  encoding  for human  recombinant  IL-6 and  methods  for its
production  which  has  been  exclusively  licensed  on a  worldwide  basis to a
pharmaceutical company. The Company has entered into a settlement agreement with
such pharmaceutical company whereby the pharmaceutical company has agreed not to
enforce its patent  against the Company  based on the Company's use of its IL-6m
patent or patent applications.

      The Company is aware that third parties have filed patent  applications in
areas  that  could  affect  the  ability  of the  Company  or its  licensee  for
diagnostics,  Abbott, to commercialize the Company's diagnostic products.  These
areas could include target  amplification  technology  and signal  amplification
technology.  Third  party  patents  have  already  issued in the field of target
amplification such as polymerase chain reaction technology (also known as PCR).

      There has been significant  litigation in the  biopharmaceutical  industry
regarding  patents and other  proprietary  rights.  Such litigation has consumed
substantial  resources for the parties involved.  If the Company became involved
in similar  litigation  regarding its intellectual  property rights, the cost of
such litigation could be substantial and could have a material adverse effect on
the Company.

      Certain proprietary trade secrets and unpatented know-how are important to
the Company in conducting its research and development activities.  There can be
no  assurance  that  others may not  independently  develop  the same or similar
technologies.  Although the Company has taken  steps,  including  entering  into
confidentiality  agreements with its employees and third parties, to protect its
trade secrets and unpatented know-how, third parties nonetheless may gain access
to such information.

      Reliance on and Attraction and Retention of Key Personnel and Consultants.

      The Company's ability to successfully  develop marketable  products and to
maintain a  competitive  position  will  depend in large part on its  ability to
attract and retain highly qualified  scientific and management  personnel and to
develop and  maintain  relationships  with  leading  research  institutions  and
consultants.  The Company is highly dependent upon the principal  members of its
management, scientific staff and Scientific Advisory Board. Competition for such
personnel and  relationships is intense,  and there can be no assurance that the
Company will be able to continue to attract and retain such personnel.

      Technological Change and Risk of Obsolescence; Competition.

      The  biopharmaceutical  industry  is  subject  to  rapid  and  significant
technological  change.  The Company has numerous  competitors,  including  major
pharmaceutical  and  chemical  companies,   specialized   biotechnology   firms,
universities and other research  institutions.  These competitors may succeed in
developing  technologies and products that are more effective than any which are
being  developed by the Company or which would render the  Company's  technology
and  products  obsolete  and  non-competitive.  Many of these  competitors  have
substantially  greater  financial and technical  resources  and  production  and
marketing  capabilities  than the Company.  In addition,  many of the  Company's
competitors  have   significantly   greater   experience  than  the  Company  in
pre-clinical testing and human clinical trials of new or improved pharmaceutical
products  and in  obtaining  Food  and Drug  Administration  ("FDA")  and  other
regulatory approvals on products for use in health care. The Company is aware of
various products under  development or manufactured by competitors that are used
for the prevention,  diagnosis or treatment of certain  diseases the Company has
targeted for product development,  some of which use therapeutic approaches that
compete directly with certain of the Company's product  candidates.  The Company
has limited  experience  in  

                                       11
conducting and managing the pre-clinical testing necessary to enter the clinical
trials  that are  required  to  obtain  government  approvals,  and has  limited
experience in conducting clinical trials. Accordingly, the Company's competitors
may succeed in  obtaining  FDA  approval  for  products  more  rapidly  than the
Company,  which could adversely affect the Company's  ability to further develop
and market its products. If the Company commences  significant  commercial sales
of its  products,  it will  also be  competing  with  respect  to  manufacturing
efficiency and marketing capabilities, areas in which the Company has limited or
no experience.

      Extensive Government Regulation.

      Research, pre-clinical development,  clinical trials and the manufacturing
and marketing of therapeutic  and diagnostic  products under  development by the
Company  are  subject to  extensive  and  rigorous  regulation  by  governmental
authorities in the United States and other  countries.  Clinical  trials and the
manufacturing  and  marketing  of  products  will be subject to the  testing and
approval processes of the FDA and comparable foreign regulatory authorities. The
process  of  obtaining  such  required  regulatory  approvals  for the  types of
products  under  development  by the  Company  usually  takes  many years and is
expensive.  Development  of a new biologic  therapeutic  or vaccine  product may
take, from initiation of clinical trials until FDA approval,  an average of five
to ten years (or more), while in vitro diagnostics may take approximately two to
six years, or more,  depending on the  requirements  of the approval  process or
clinical data  requirements.  If the FDA requests  additional  data,  these time
periods can be  substantially  increased.  Even after such  additional  data are
submitted,  there can be no assurance of obtaining  FDA  approval.  In addition,
product approvals may be withdrawn or limited for noncompliance  with regulatory
standards or the occurrence of unforeseen  problems following initial marketing.
The Company has not sought or received  regulatory  approval for the  commercial
sale of any of its products or for any  manufacturing  processes or  facilities.
The Company and its  licensees  may  encounter  significant  delays or excessive
costs in their  respective  efforts to secure  necessary  approvals or licenses.
Future federal, state, local or foreign legislative or administrative acts could
also prevent or delay  regulatory  approval of the  Company's or its  licensees'
products.  There  can be no  assurance  that the  Company  or its  collaborative
partners  will be able to obtain the necessary  approvals for clinical  testing,
manufacturing or marketing of the Company's products,  or that the clinical data
they obtain in clinical  studies will be  sufficient to establish the safety and
effectiveness  of  the  products.   Failure  to  obtain  or  maintain  requisite
governmental  approvals or failure to obtain approvals of the clinical  intended
uses  requested,  could delay or  preclude  the  Company or its  licensees  from
further developing particular products or from marketing their products or could
limit the  commercial  use of the products  and thereby have a material  adverse
effect on the Company's liquidity and financial condition.

      Product Liability Exposure.

      The use of the  Company's  product  candidates  during  testing  or  after
approval  entails an inherent  risk of adverse  effects  which could  expose the
Company to product liability claims.  There can be no assurance that the Company
would have sufficient resources to satisfy any liability resulting from any such
claims.  The  Company  endeavors  to  obtain  indemnification  by its  corporate
partners against certain of such claims. However, there can be no assurance that
such  parties will honor,  or have the  financial  resources to honor,  any such
obligations.  The Company currently has product liability insurance which covers
products in pre-clinical  and clinical  testing.  There can be no assurance that
such coverage will be adequate in scope to protect the Company in the event of a
successful product liability claim.

      Hazardous Materials; Environmental Matters.

      The Company's  research and development  activities involve the controlled
use  of  hazardous  materials,   chemicals,   viruses  and  various  radioactive
compounds.  The  Company  is  subject  to  federal,  state  and  local  laws and
regulations  governing the use, manufacture,  storage,  handling and disposal of
such materials and certain waste  products.  Although the Company  believes that
its safety  procedures for handling and disposing of such materials  comply with
the standards  prescribed by such laws and  regulations,  the risk of accidental
contamination or injury from these materials cannot be completely eliminated. In
the event of such an accident,  the Company could be held liable for any damages
that result,  and any such liability  could exceed the resources of the Company.
The  Company  may  be  required  to  incur  significant  costs  to  comply  with
environmental  laws and  regulations  in the future.  The Company's  operations,
business or assets may be materially or adversely  affected by current or future
environmental laws or regulations.

                                       12
Uncertainty of Health Care Reimbursement and Related Matters.

      The  Company's  ability to earn  sufficient  returns on its  products  may
depend  in part on the  extent  to  which  reimbursement  for the  costs of such
products and related treatments will be available to purchasers or users thereof
from  government  health  administration  authorities,  private health  coverage
insurers  and  other  organizations.  If  purchasers  or users of the  Company's
products are not entitled to adequate  reimbursement  for the cost of using such
products,  they may forego or reduce such use. Significant uncertainty exists as
to the  reimbursement  status of newly approved health care products,  and there
can be no assurance that adequate third-party coverage will be available.

      Possible Volatility of Stock Price.

      The Company  believes  that  factors such as the status of its products in
development,   announcements  of  new  products,  formation  or  termination  of
corporate  alliances,  other developments by the Company, its competitors or the
FDA,  determinations  in connection  with patent  applications of the Company or
others and variations in quarterly operating results,  among others, could cause
the market price for the Common Stock to fluctuate  substantially.  In addition,
the stock market has experienced extreme price and volume fluctuations that have
particularly   affected   the  market  price  for  many  high   technology   and
healthcare-related companies and that have often been unrelated to the operating
performance of these  companies.  These broad market  fluctuations may adversely
affect the market price of the Common Stock.

      Limitations on Net Operating Loss Carryforwards.

      At December 31, 1997, the Company had net operating loss carryforwards for
federal  income tax  purposes  of  approximately  $115,000,000  which  expire at
various  dates from 2000  through  2012.  At  December  31, 1997 the Company had
research  credit  carryforwards  of  approximately  $2,303,000  which  expire at
various  dates from 2001 through  2012.  Pursuant to Section 382 of the Internal
Revenue Code of 1986,  as amended,  the annual  utilization  of a company's  net
operating loss and research credit  carryforwards may be limited if such company
experiences  a change in ownership of more than 50  percentage  points  within a
three-year  period.  Since 1986, the Company has  experienced two such ownership
changes.  Accordingly,  the Company's net operating loss carryforwards available
to offset future federal  taxable  income arising before such ownership  changes
are limited to  $5,159,000  annually.  Similarly,  the Company is  restricted in
using its research credit carryforwards arising before such ownership changes to
offset future federal income tax expense.

      Dividend Policy and Restrictions.

      The Company has never paid any cash  dividends  on its Common  Stock.  The
Board of Directors of the Company will determine future dividend policy based on
the Company's results of operations,  financial condition,  capital requirements
and other circumstances. The Company does not anticipate that any dividends will
be  declared on its Common  Stock in the  foreseeable  future.  Except as may be
utilized to pay the dividends payable on the Company's Series A Preferred Stock,
any  earnings  which the  Company  may  realize  will be retained to finance the
growth of the Company.  In addition,  the terms of the Series A Preferred  Stock
restrict  the payment of  dividends  on other  classes and series of stock.  See
"Prospectus    Summary-The    Company-BEC2    Cancer    Vaccine"    and    "Risk
Factors-Dilution."

                                 USE OF PROCEEDS

      The  Company  will not receive  any  proceeds  from the sale of the Shares
offered herein by the Selling Stockholders, however, the Company has received or
will  receive the  exercise  price for Options  and  Warrants  upon the prior or
future exercise by such Selling  Stockholders  of such Options and Warrants.  If
all of the Options and Warrants held by Selling  Stockholders  as of the date of
this Prospectus and covered by this  Prospectus are exercised,  the Company will
receive  aggregate  estimated  proceeds  (including any amounts  received by the
Company in  connection  with the previous  exercise by Selling  Stockholders  of
Options and  Warrants  prior to the date of this  Prospectus)  of  approximately
$17,562,000.  The Company anticipates utilizing any such proceeds received,  and
has utilized any such proceeds  previously  received,  upon the exercise of such
Options  and  Warrants  (i) to  continue  to fund and  expand its  research  and
development programs and (ii) for general corporate purposes,  including working
capital. There can be no assurance that any of the Options will be exercised.

                                       13
SELLING STOCKHOLDERS

      This Prospectus covers possible sales by the Selling Stockholders, who are
officers and directors of the Company who may be "affiliates" of the Company (as
such term is defined  under Rule 405 under the  Securities  Act), of Shares that
such Selling  Stockholders have acquired and/or may acquire through the exercise
of Options granted under the Plans and/or  Warrants.  The names of such officers
and  directors  who may be  Selling  Stockholders  from time to time are  listed
below,  along with, as of September 25, 1998, (i) the number of shares of Common
Stock currently owned by each such person,  (ii) the number of Shares offered by
each such person for sale hereby and (iii) the number of shares of Common  Stock
to be owned by each such Selling  Stockholder  following  the  completion of the
offering  contemplated  hereby and the percentage  that such shares will bear to
the number of  outstanding  shares of Common  Stock at such time.  The number of
Shares  offered for sale by such  individuals  may be updated in, and additional
individuals  who  are  affiliates  of  the  Company  may  be  added  as  Selling
Stockholders  hereunder by, supplements to this Prospectus,  which will be filed
with the Commission in accordance  with Rule 424(b) under the Securities Act. In
reliance  upon  Item  2(b) of  General  Instruction  C to  Form  S-8  under  the
Securities  Act,  the  officers  and  directors  of the Company  listed below as
Selling  Stockholders have been listed herein whether or not such persons have a
present  intent to reoffer or resell any or all of the Shares listed as owned by
them and being offered hereby.

                                                       Number       Percentage 
                                                     of Shares       of Shares
                         Number           Number    Beneficially   Beneficially
                        of Shares       of Shares   Owned After    Owned After 
                       Beneficially      Offered    Completion of Completion of
Selling Stockholder(1)   Owned(2)       Hereby(3)    Offering(4)    Offering(4)
----------------------   --------       ---------    -----------    -----------

Richard Barth             41,500(5)       40,000(5)      1,500          *   
                                                                        
Dr. Jean Carvais          48,542(6)       48,542(6)          0          *
                                                                        
Vincent T. DeVita, Jr     90,842(7)       90,542(7)        300          *
                                                                        
Robert F. Goldhammer     836,576(8)      183,232(8)    653,344          2.41%
                                                                        
Carl S. Goldfischer      375,000(9)      375,000(9)          0          *
                                                                        
David M. Kies           107,000(10)      41,397(10)     65,603          *
                                                                        
Paul B. Kopperl          70,960(11)      49,960(11)     21,000          *
                                                                        
John Mendelsohn         212,226(12)     212,226(12)          0          *
                                                                        
William Miller           42,397(13)      41,397(13)      1,000          *
                                                                        
Harlan Waksal         1,245,780(14)     411,578(14)    834,202          3.07%
                                                                        
Samuel Waksal         1,467,583(15)   1,359,000(15)    108,583          *
                                                                     
----------
*     Less than 1%.

(1)   Notwithstanding  their  respective  inclusion  in this  table  as  Selling
      Stockholders, the individuals listed in this table expressly disclaim that
      they are affiliates of the Company.

(2)   Assumes that all options or warrants to acquire  Common Stock held by such
      Selling  Stockholder  are  exercisable  within 60 days of the date of this
      Prospectus.

(3)   Assumes that all Options and Warrants held by such Selling Stockholder are
      fully exercisable for the underlying Shares.

(4)   Assumes the sale of all Shares offered by all Selling  Stockholders  under
      this Prospectus, and that all options and warrants to acquire Common Stock
      held by such Selling  Stockholders  are exercisable  within 60 days of the
      date of the  completion of the offering.  As the Company is unable,  as of
      the date of this  Prospectus,  to determine the date of the  completion of
      the  offering  hereunder,  the  number of  shares  and  percentages  shown
      hereunder are computed with reference to the aggregate number of shares of
      Common Stock of the Company  issued and  outstanding  as of September  25,
      1998 and giving effect to the exercise of the Options and Warrants. Shares
      of the Company's Series A Convertible Preferred Stock are not included, as
      no voting rights are attached to such shares.

                                       14
(5)      Includes an aggregate of 40,000  Shares  subject to Options  granted to
         Mr.  Barth   pursuant  to  the  ImClone   Systems   Incorporated   1996
         Non-Qualified Stock Option Plan. Mr. Barth is a director of the Company

(6)      Includes (i) an aggregate of 20,542 Shares  subject to Options  granted
         to Dr.  Carvais  pursuant  to the  ImClone  Systems  Incorporated  1986
         Non-Qualified  Stock Option Plan and (ii) an aggregate of 28,000 Shares
         subject  to Options  granted to Dr.  Carvais  pursuant  to the  ImClone
         Systems  Incorporated 1996 Non-Qualified Stock Option Plan. Dr. Carvais
         is a director of the Company.

(7)      Includes (i) an aggregate of 48,542 Shares  subject to Options  granted
         to  Dr.  DeVita  pursuant  to the  ImClone  Systems  Incorporated  1986
         Non-Qualified  Stock  Option Plan,  (ii) an aggregate of 20,000  Shares
         previously  acquired by Mr. DeVita upon the exercise of Options granted
         thereto pursuant to the ImClone Systems Incorporated 1986 Non-Qualified
         Stock Option Plan,  and (iii) an aggregate of 22,000 Shares  subject to
         Options   granted  to  Mr.  DeVita  pursuant  to  the  ImClone  Systems
         Incorporated  1996  Non-Qualified  Stock Option Plan.  Dr.  DeVita is a
         director of the Company.

(8)      Includes (i) an aggregate of 8,542 Shares subject to Options granted to
         Mr.  Goldhammer  pursuant  to the  ImClone  Systems  Incorporated  1986
         Non-Qualified  Stock Option Plan,  (ii) an aggregate of 105,000  Shares
         subject to Options  granted to Mr.  Goldhammer  pursuant to the ImClone
         Systems  Incorporated 1996 Non-Qualified Stock Option Plan and (iii) an
         aggregate  of  69,690  Shares   subject  to  Warrants   issued  to  Mr.
         Goldhammer.  The  additional  shares of Common  Stock  listed under the
         column "Number of Shares  Beneficially  Owned" include 13,314 shares of
         Common  Stock  held in  trust,  as to which  Mr.  Goldhammer  disclaims
         beneficial  ownership.  Mr. Goldhammer is the Chairman of the Company's
         Board of Directors.

(9)      Includes (i) an aggregate of 350,000 Shares subject to Options  granted
         to Dr.  Goldfischer  pursuant to the ImClone Systems  Incorporated 1996
         Non-Qualified  Stock Option Plan and (ii) an aggregate of 25,000 Shares
         subject to Options granted to Dr.  Goldfischer  pursuant to the ImClone
         Systems  Incorporated 1996 Incentive Stock Option Plan. Dr. Goldfischer
         is the Company's Vice President, Finance and Chief Financial Officer.

(10)     Includes (i) an aggregate of 25,000 Shares  subject to Options  granted
         to  Mr.  Kies  pursuant  to  the  ImClone  Systems   Incorporated  1996
         Non-Qualified  Stock Option Plan and (ii) an aggregate of 16,397 Shares
         previously  acquired by Mr. Kies upon the  exercise of Options  granted
         thereto pursuant to the ImClone Systems Incorporated 1996 Non-Qualified
         Stock Option Plan. The  additional  shares of Common Stock listed under
         the column "Number of Shares  Beneficially  Owned" include 6,000 shares
         of Common Stock held by Mr. Kies as custodian  for his son, as to which
         Mr. Kies disclaims beneficial ownership.  Mr. Kies is a director of the
         Company.

(11)     Includes (i) an aggregate of 7,500 Shares subject to Options granted to
         Mr.  Kopperl  pursuant  to  the  ImClone  Systems   Incorporated   1986
         Non-Qualified  Stock Option Plan and (ii) an aggregate of 40,000 Shares
         subject  to Options  granted to Mr.  Kopperl  pursuant  to the  ImClone
         Systems   Incorporated  1996  Non-Qualified   Stock  Option  Plan.  The
         additional  shares of Common Stock  listed under the column  "Number of
         Shares  Beneficially  Owned" include 500 shares of Common Stock held by
         Mr.  Kopperl's  spouse as to which  Mr.  Kopperl  disclaims  beneficial
         ownership. Mr. Kopperl is a director of the Company.

(12)     Includes (i) an aggregate of 120,000 Shares subject to Options  granted
         to Dr.  Mendelsohn  pursuant to the ImClone Systems  Incorporated  1986
         Non-Qualified  Stock Option Plan and (ii) an aggregate of 92,226 Shares
         subject to Options  granted to Dr.  Mendelsohn  pursuant to the ImClone
         Systems   Incorporated  1996  Non-Qualified   Stock  Option  Plan.  Dr.
         Mendelsohn is a director of the Company.

(13)     Includes an aggregate of 41,397  Shares  subject to Options  granted to
         Mr.  Miller   pursuant  to  the  ImClone  Systems   Incorporated   1996
         Non-Qualified  Stock  Option  Plan.  Mr.  Miller is a  director  of the
         Company.

(14)     Includes (i) an aggregate of 390,000 Shares subject to Options  granted
         to  Dr.  Waksal  pursuant  to the  ImClone  Systems  Incorporated  1996
         Non-Qualified  Stock Option Plan and the ImClone  Systems  Incorporated
         1996  Incentive  Stock Option  Plan,  (ii) an aggregate of 3,180 Shares
         subject to  Warrants  issued to Dr.  Waksal and (iii) an  aggregate  of
         18,398  Shares  previously  acquired by Dr. Waksal upon the exercise of
         Options  granted thereto  pursuant to the ImClone Systems  Incorporated
         1986  Non-Qualified  Stock  Option  Plan.  Dr.  Harlan  Waksal  is  the
         Company's  Executive Vice President and Chief  Operating  Officer and a
         director of the Company.  Dr.  Harlan  Waksal and Dr. Samuel Waksal are
         brothers.

(15)     Includes (i) an aggregate of 75,000 Shares  subject to Options  granted
         to  Dr.  Waksal  pursuant  to the  ImClone  Systems  Incorporated  1986
         Non-Qualified  Stock Option Plan,  (ii) an aggregate of 595,000  Shares
         subject to Options granted

                                       15
to  Dr.  Waksal  pursuant  to the  ImClone  Systems  Incorporated  1996
         Non-Qualified  Stock Option Plan and the ImClone  Systems  Incorporated
         1996 Incentive Stock Option Plan,  (iii) an aggregate of 350,000 Shares
         subject  to  Warrants  issued to Dr.  Waksal and (iv) an  aggregate  of
         339,000 Shares  previously  acquired by Dr. Waksal upon the exercise of
         Warrants issued thereto.  Dr. Samuel Waksal is the Company's  President
         and Chief  Executive  Officer.  Dr. Samuel Waksal and Dr. Harlan Waksal
         are brothers.

                              PLAN OF DISTRIBUTION

      The Shares,  which have been issued  and/or are issuable upon the exercise
of the  Options or  Warrants  may be sold  pursuant  to this  Prospectus  by the
Selling Stockholders. These sales may occur in privately negotiated transactions
or in the over-the-counter  market through brokers and dealers, as agents, or to
brokers and dealers,  as principals who may receive  compensation in the form of
discounts,  concessions or commissions from the Selling Stockholders or from the
purchasers of the Common Stock for whom the  broker-dealers  may act as agent or
to whom they may sell as principal,  or both. After the passage of the requisite
period of time, the Selling  Stockholders  may also sell the Shares  pursuant to
Rule 144.  The Company has been  advised by the Selling  Stockholders  that they
have not made any arrangements  relating to the  distribution of the Shares.  In
effecting sales,  broker-dealers  engaged by the Selling Stockholder may arrange
for other broker-dealers to participate. Broker-dealers will receive commissions
or  discounts  from  the  Selling   Stockholder  in  amounts  to  be  negotiated
immediately prior to the sale.

      Upon being notified by a Selling Stockholder that any material arrangement
(other than a customary  brokerage account agreement) has been entered into with
a broker or dealer for the sale of Shares pursuant to this Prospectus  through a
block trade, purchase by a broker or dealer, or similar transaction, the Company
will file a supplemented Prospectus pursuant to Rule 424(c) under the Securities
Act disclosing (a) the name of each such broker-dealer, (b) the number of Shares
involved, (c) the price at which such Shares were sold, (d) the commissions paid
or discounts or concessions allowed to such broker-dealer(s), (e) if applicable,
that such  broker-dealer(s)  did not  conduct  any  investigation  to verify the
information  set  out  or  incorporated  by  reference  in  the  Prospectus,  as
supplemented, and (f) any other facts material to the transaction.

      The Selling  Stockholders and any broker-dealers who execute sales for the
Selling  Stockholders may be deemed to be  "underwriters"  within the meaning of
the  Securities Act by virtue of the number of shares of Common Stock to be sold
or resold by such persons or entities or the manner of sale thereof, or both. If
the Selling  Stockholders or any  broker-dealer or other holders were determined
to be underwriters,  any discounts,  concessions or commissions received by them
or by brokers or dealers acting on their behalf and any profits received by them
on the  resale  of their  shares of Common  Stock  might be deemed  underwriting
discounts and commissions under the Securities Act.

      The Selling Stockholders have represented to the Company that any purchase
or sale of the Common  Stock by them will be in  compliance  with  Regulation  M
("Regulation M") promulgated under the Exchange Act. In general,  Rule 102 under
Regulation M prohibits any person connected with a distribution of the Company's
Common Stock (the  "Distribution")  from directly or indirectly  bidding for, or
purchasing  for any account in which he has a  beneficial  interest,  any Common
Stock or any right to purchase  Common  Stock,  for a period of one business day
prior to and subsequent to completion of his  participation  in the Distribution
(the "Distribution Period").

      During the Distribution  Period,  Rule 104 ("Rule 104") under Regulation M
prohibits  the  Selling  Stockholders  and  any  other  persons  engaged  in the
Distribution from engaging in any stabilizing bid or purchasing the Common Stock
except for the purpose of  preventing  or retarding a decline in the open market
price of the Common Stock. No such person may effect any stabilizing transaction
to facilitate  any offering at the market.  Inasmuch as any Selling  Stockholder
will be  reoffering  and  reselling  the Common  Stock at the  market,  Rule 104
prohibits him or her from effecting any stabilizing transaction in contravention
of Rule 104 with respect to the Common Stock.

                                  LEGAL MATTERS

      Certain  legal  matters in  connection  with the sale and  validity of the
Shares  will be passed upon for the Company by Kaye,  Scholer,  Fierman,  Hays &
Handler, LLP.

                                       16
DISCLOSURE OF COMMISSION POSITION ON
                 INDEMNIFICATION FOR SECURITIES ACT LIABILITIES

      The  Company's   Certificate  of  Incorporation  and  Bylaws  provide  for
indemnification  of officers and directors in instances,  among others, in which
they acted in good faith and in a manner they  reasonably  believed to be in, or
not opposed to, the best interests of the Company and in which,  with respect to
criminal proceedings,  they had no reasonable cause to believe their conduct was
unlawful.

      Insofar as  indemnification  for liabilities  arising under the Securities
Act of 1933 may be permitted to directors,  officers and controlling  persons of
the Company pursuant to the foregoing provisions,  or otherwise, the Company has
been  advised  that in the opinion of the  Commission  such  indemnification  is
against  public  policy as expressed in the  Securities  Act and is,  therefore,
unenforceable.

                                       17
PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

      The   contents  of  ImClone   Systems   Incorporated's   (the   "Company")
Registration Statement on Form S-8, File No.333-10275, filed with the Securities
and Exchange  Commission (the  "Commission") on August 15, 1996 are incorporated
herein by reference.

Item 8.       Exhibits.

Exhibit No.   Description
-----------   -----------

5.1           Opinion  of  Kaye,  Scholer,  Fierman,  Hays &  Handler,  LLP with
              respect to the legality of the securities being registered. (Filed
              herewith).

23.1          Consent of KPMG Peat Marwick LLP. (Filed herewith).

23.2          Consent of Kaye, Scholer,  Fierman, Hays & Handler, LLP. (Included
              in Exhibit 5.1).

24.           Power  of  Attorney.   (Included   on  signature   pages  to  this
              Registration Statement).

99.1          ImClone Systems  Incorporated 1996 Incentive Stock Option Plan, As
              Amended. (Incorporated by reference to Exhibit No. 99.1 of ImClone
              Systems  Incorporated's  Quarterly  Report  of Form  10-Q  for the
              fiscal quarter ended June 30, 1997).

99.2          ImClone Systems Incorporated 1996 Non-Qualified Stock Option Plan,
              As Amended.  (Incorporated by reference to Exhibit 99.2 of ImClone
              Systems  Incorporated's  Quarterly  Reporting  Form  10-Q  for the
              fiscal quarter ended June 30, 1997).

                                       18
SIGNATURES

      Pursuant to the requirements of the Securities Act of 1933, the Registrant
certifies  that it has  reasonable  grounds to believe  that it meets all of the
requirements  for  filing  on Form S-8 and has  duly  caused  this  Registration
Statement  to be  signed  on its  behalf  by  the  undersigned,  thereunto  duly
authorized,  in the  City of New  York,  State of New  York,  on the 30th day of
September 1998.

                                  IMCLONE SYSTEMS INCORPORATED

                                  By: /s/  Samuel D. Waksal
                                      ----------------------------------------
                                      Samuel D. Waksal
                                      President and Chief Executive Officer

      Pursuant  to  the  requirements  of  the  Securities  Act  of  1933,  this
Registration  Statement  has been signed below by the  following  persons in the
capacities and on the dates indicated.  Each person whose  individual  signature
appears below hereby authorizes  Samuel D. Waksal,  Harlan W. Waksal and John B.
Landes, or any of them, to execute in the name and on behalf of each such person
and to file any amendment to this Registration Statement, and appoints Samuel D.
Waksal, Harlan W. Waksal and John B. Landes, or any of them, as attorney-in-fact
to sign on his behalf  individually  and in each capacity  stated below,  and to
file  any  amendments  to this  Registration  Statement,  including  any and all
post-effective amendments.

        Signature                     Title                          Date
        ---------                     -----                          ----

/s/  Robert F. Goldhammer    Chairman of the Board            September 30, 1998
-------------------------    and Director
Robert F. Goldhammer

/s/ Samuel D. Waksal         President, Chief Executive       September 30, 1998
-------------------------    Officer
Samuel D. Waksal             and Director
                             (Principal Executive Officer)

/s/  Harlan W. Walsal        Executive Vice President,        September 30, 1998
-------------------------    Chief Operating 
Harlan W. Waksal             Officer and Director

/s/  Carl Goldfischer        Vice President of Finance        September 30, 1998
-------------------------    and Chief Financial
Carl Goldfischer             Officer (Principal
                             Financial and Accounting 
                             Officer)

/s/  Jean Carvais            Director                         September 30, 1998
-------------------------
Jean Carvais

/s/ Vincent T. DeVita, Jr.   Director                         September 30, 1998
--------------------------
Vincent T. DeVita, Jr.

/s/  Paul B. Kopperl         Director                         September 30, 1998
-------------------------
Paul B. Kopperl

/s/  William R. Miller       Director                         September 30, 1998
-------------------------
William R. Miller

/s/  Davis M. Kies           Director                         September 30, 1998
-------------------------
David M. Kies

/s/  John Mendelsohn         Director                         September 30, 1998
-------------------------
John Mendelsohn

/s/  Richard Barth           Director                         September 30, 1998
-------------------------
Richard Barth

                                       S-1
EXHIBIT INDEX

Exhibit
No.                        Description
---                        -----------

5.1       Opinion of Kaye, Scholer, Fierman, Hays & Handler, LLP with respect to
          the legality of the securities being registered. (Filed herewith).

23.1      Consent of KPMG Peat Marwick LLP. (Filed herewith).

23.2      Consent of Kaye, Scholer,  Fierman,  Hays & Handler, LLP. (Included in
          Exhibit 5.1).

24.       Power of Attorney.  (Included on signature pages to this  Registration
          Statement).

99.1      ImClone  Systems  Incorporated  1996  Incentive  Stock Option Plan, As
          Amended.  (Incorporated  by  reference  to Exhibit No. 99.1 of ImClone
          Systems  Incorporated's  Quarterly  Report of Form 10-Q for the fiscal
          quarter ended June 30, 1997).

99.2      ImClone Systems  Incorporated 1996 Non-Qualified Stock Option Plan, As
          Amended. (Incorporated by reference to Exhibit 99.2 of ImClone Systems
          Incorporated's  Quarterly  Reporting  Form 10-Q for the fiscal quarter
          ended June 30, 1997).