<PAGE>


    As filed with the Securities and Exchange Commission on January 16, 2001
                                                   Registration No. 333-
================================================================================


                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549


                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933


                           VION PHARMACEUTICALS, INC.
             (Exact name of registrant as specified in its charter)

            DELAWARE                                       13-3671221
     (State or other juris-                             (I.R.S. Employer
    diction of incorporation                             Identification
         or organization)                                    Number)

                                 4 SCIENCE PARK
                          NEW HAVEN, CONNECTICUT 06511
                                 (203) 498-4210
          (Address, including zip code, and telephone number, including
            area code, of registrant's principal executive offices)

                           VION PHARMACEUTICALS, INC.
                        2000 EMPLOYEE STOCK PURCHASE PLAN
                            (full title of the plan)

                                  ALAN KESSMAN
                      PRESIDENT AND CHIEF EXECUTIVE OFFICER
                           VION PHARMACEUTICALS, INC.
                                 4 SCIENCE PARK
                          NEW HAVEN, CONNECTICUT 06511
                                 (203) 498-4210
            (Name, address, including zip code, and telephone number,
                   including area code, of agent for service)

       Copies of all communications, including all communications sent to
                   the agent for service, should be sent to:

                                PAUL JACOBS, ESQ.
                            LAWRENCE A. SPECTOR, ESQ.
                           FULBRIGHT & JAWORSKI L.L.P.
                                666 FIFTH AVENUE
                            NEW YORK, NEW YORK 10103
                                 (212) 318-3000

                         CALCULATION OF REGISTRATION FEE
<TABLE>
<CAPTION>
----------------------------------------------------------------------------------------------------------------------------
TITLE OF SECURITIES TO BE        AMOUNT TO BE    PROPOSED MAXIMUM             PROPOSED MAXIMUM              AMOUNT OF
REGISTERED                       REGISTERED(1)   OFFERING PRICE PER UNIT      AGGREGATE OFFERING PRICE(2)   REGISTRATION FEE
----------------------------------------------------------------------------------------------------------------------------
<S>                              <C>             <C>                          <C>                           <C>
COMMON STOCK $0.01 PAR VALUE
PER SHARE....................    450,000 SHARES  $7.836                       $3,526,200                    $881.55
============================================================================================================================
</TABLE>

(1) Plus such additional indeterminable number of shares as may be required
pursuant to the Vion Pharmaceuticals, Inc. 2000 Employee Stock Purchase Plan in
the event of a stock dividend, stock split, recapitalization or other similar
change in the Common Stock.

(2) Computed in accordance with Rule 457(h) under the Securities Act of 1933, as
amended, such computation is based on $7.836 per share (85% of the average of
the high and the low prices of the registrant's common stock as reported on the
Nasdaq National Market on January 12, 2001). Pursuant to the Vion
Pharmaceuticals, Inc. Employee Stock Purchase Plan, shares are sold at 85% of
the lesser of the fair market value of such shares on the first day of an
offering period or the last day of the applicable purchase period.



<PAGE>

                                     PART I

                     INFORMATION REQUIRED IN THE PROSPECTUS

         In accordance with the rules and regulations of the Securities and
Exchange Commission (the "Commission"), the documents containing the information
called for in Part I of Form S-8 will be sent or given to individuals who
participate in the 2000 Employee Stock Purchase Plan adopted by Vion
Pharmaceuticals, Inc. (the "Company" or the "Registrant") and are not being
filed with or included in this Form S-8.





<PAGE>


                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3.           INCORPORATION OF DOCUMENTS BY REFERENCE

                  The following documents filed by the Company are incorporated
herein by reference:

(i)   The Company's Annual Report on Form 10-KSB for the fiscal year ended
December 31, 1999.

(ii)  The Company's Quarterly Reports on Form 10-Q for the quarters ended March
31, 2000, June 30, 2000 and September 30, 2000.

(iii) The Company's Current Reports on Form 8-K filed on February 14, 2000,
March 28, 2000, June 22, 2000, November 8, 2000, November 13, 2000, December 1,
2000 and January 11, 2001.

(iv)  The Company's Proxy Statement on Schedule DEFR14A filed on September 19,
2000.

(v)   The description of the Company's Common Stock contained in Item 1 of the
Company's Registration Statement on Form 8-A filed July 31, 1995.

                  In addition to the foregoing, all documents subsequently filed
by the Company pursuant to Sections 13(a), 13(c), 14 and 15(d) of the Securities
Exchange Act of 1934, prior to the filing of a post-effective amendment
indicating that all of the securities offered hereunder have been sold or
deregistering all securities then remaining unsold, shall be deemed to be
incorporated by reference in this Registration Statement and to be part hereof
from the date of filing of such documents. Any statement contained in a document
incorporated by reference in this Registration Statement shall be deemed to be
modified or superseded for purposes of this Registration Statement to the extent
that a statement contained herein or in any subsequently filed document that is
also incorporated by reference herein modifies or supersedes such statement. Any
statement so modified or superseded shall not be deemed, except as so modified
or superseded, to constitute a part of this Registration Statement.

ITEM 4.           DESCRIPTION OF SECURITIES

                  Not applicable.

ITEM 5.           INTERESTS OF NAMED EXPERTS AND COUNSEL

                  Not applicable.





                                       2







<PAGE>


ITEM 6.           INDEMNIFICATION OF DIRECTORS AND OFFICERS

                  Under the General Corporation Law of the State of Delaware
("DGCL"), a corporation may include provisions in its certificate of
incorporation that will relieve its directors of monetary liability for breaches
of their fiduciary duty to the corporation, except under certain circumstances,
including a breach of the director's duty of loyalty, acts or omissions of the
director not in good faith or which involve intentional misconduct or a knowing
violation of law, the approval of an improper payment of a dividend or an
improper purchase by the corporation of stock or any transaction from which the
director derived an improper personal benefit. The registrant's Restated
Certificate of Incorporation, as amended, eliminates the personal liability of
directors to the registrant or its stockholders for monetary damages for breach
of fiduciary duty as a director with certain limited exceptions set forth in the
DGCL.

                  Section 145 of the DGCL grants to corporations the power to
indemnify each officer and director against liabilities and expenses incurred by
reason of the fact that he or she is or was an officer or director of the
corporation if he or she acted in good faith and in a manner he or she
reasonably believed to be in or not opposed to the best interests of the
corporation and, with respect to any criminal action or proceeding, had no
reasonable cause to believe his or her conduct was unlawful. The registrant's
Restated Certificate of Incorporation, as amended, and Bylaws provide for
indemnification of each officer and director of the registrant to the fullest
extent permitted by the DGCL. Section 145 of the DGCL also empowers corporations
to purchase and maintain insurance on behalf of any person who is or was an
officer or director of the corporation against liability asserted against or
incurred by him in any such capacity, whether or not the corporation would have
the power to indemnify such officer or director against such liability under the
provisions of Section 145. The registrant has purchased and maintains a
directors' and officers' liability policy for such purposes.

ITEM 7.           EXEMPTION FROM REGISTRATION CLAIMED

                  Not Applicable.

ITEM 8.           EXHIBITS

<TABLE>
        <S>       <C>
         4.1      --    Vion Pharmaceuticals, Inc. 2000 Employee Stock Purchase
                        Plan

         5.1      --    Opinion of Fulbright & Jaworski L.L.P.

         23.1     --    Consent of Ernst & Young LLP

         23.2     --    Consent of Fulbright & Jaworski L.L.P. (included in
                        Exhibit 5.1)

         24.1     --    Power of Attorney (included in signature page)

ITEM 9.           UNDERTAKINGS

         (a) The undersigned Registrant hereby undertakes:





                                       3





<PAGE>

                  (1) To file, during any period in which offers or sales are
being made, a post-effective amendment to this Registration Statement:

                           (i)      To include any prospectus required by
section 10(a)(3) of the Securities Act of 1933;

                           (ii)     To reflect in the prospectus any facts or
events arising after the effective date of the registration statement (or the
most recent post-effective amendment thereof) which, individually or in the
aggregate, represent a fundamental change in the information set forth in the
registration statement. Notwithstanding the foregoing, any increase or decrease
in volume of securities offered (if the total dollar value of securities offered
would not exceed that which was registered) and any deviation from the low or
high end of the estimated maximum offering range may be reflected in the form of
prospectus filed with the Commission pursuant to Rule 424(b) if, in the
aggregate, the changes in volume and price represent no more than 20 percent
change in the maximum aggregate offering price set forth in the "Calculation of
Registration Fee" table in the effective registration statement;

                           (iii)    To include any material information with
respect to the plan of distribution not previously disclosed in the registration
statement or any material change to such information in the registration
statement;

                  (2) That, for the purpose of determining any liability under
the Securities Act of 1933, each such post-effective amendment shall be deemed
to be a new registration statement relating to the securities offered therein,
and the offering of such securities at that time shall be deemed to be the
initial bona fide offering thereof.

                  (3) To remove from registration by means of a post-effective
amendment any of the securities being registered which remain unsold at the
termination of the offering.

         (b) The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act of 1933, each filing of the
Registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Securities Exchange Act of 1934 (and, where applicable, each filing of an
employee benefit plan's annual report pursuant to Section 15(d) of the
Securities Exchange Act of 1934) that is incorporated by reference in the
registration statement shall be deemed to be a new registration statement
relating to the securities offered therein, and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.

         (c) Insofar as indemnification for liabilities arising under the
Securities Act of 1933 may be permitted to directors, officers and controlling
persons of the Registrant pursuant to the foregoing provisions, or otherwise,
the Registrant has been advised that in the opinion of the Securities and
Exchange Commission such indemnification is against public policy as expressed
in the Securities Act and is, therefore, unenforceable. In the event a claim for
indemnification against such liabilities (other than the payment by the
Registrant of expenses incurred or paid by a director, officer, or controlling
person of the Registrant in the successful defense of any action, suit or
proceeding) is asserted by such director, officer, or controlling person in
connection with






                                       4






<PAGE>

the securities being registered hereunder, the Registrant will, unless in the
opinion of its counsel the matter has been settled by controlling precedent,
submit to a court of appropriate jurisdiction the question whether such
indemnification by it is against public policy as expressed in the Act and will
be governed by the final adjudication of such issue.






                                       5




<PAGE>


                                   SIGNATURES

                  Pursuant to the requirements of the Securities Act of 1933, as
amended, 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 Haven, State of Connecticut, on January 16,
2001.



                                        VION PHARMACEUTICALS, INC.


                                        By: /s/ Alan Kessman
                                           -------------------------------------
                                           Alan Kessman
                                           President and Chief Executive Officer



                                POWER OF ATTORNEY

                  KNOW ALL MEN BY THESE PRESENTS, that each person whose
signature appears below and on the following page constitutes and appoints Alan
Kessman and Karen Schmedlin as his true and lawful attorneys-in-fact and agents,
each acting alone, with full power of substitution and resubstitution, for him
and in his name, place and stead, in any and all capacities, to sign any and all
amendments to this Registration Statement, including post-effective amendments,
and to file the same, with all exhibits thereto, and all documents in connection
therewith, with the Securities and Exchange Commission, granting unto said
attorneys-in-fact and agents, and each of them, full power and authority of do
and perform each and every act and thing requisite and necessary to be done in
and about the premises, as fully to all intents and purposes as he might or
could do in person, and hereby ratifies and confirms all that said
attorneys-in-fact and agents, each acting alone, or their substitute or
substitutes, may lawfully do or cause to be done by virtue hereof.

                  Pursuant to the requirements of the Securities Act of 1933, as
amended, this registration statement has been signed below by the following
persons in the capacities and on the dates indicated.




</TABLE>
<TABLE>
<CAPTION>
Signature                                       Title                                Date
---------                                       -----                                ----
<S>                               <C>                                         <C>
/s/ William R. Miller               Chairman of the Board                       January 16, 2001
--------------------------
William R. Miller


/s/ Alan Kessman                    President, Chief Executive                  January 16, 2001
--------------------------          Officer and Director (Principal
Alan Kessman                        Executive Officer)
</TABLE>




<PAGE>





<TABLE>
<S>                               <C>                                         <C>
/s/ Karen Schmedlin                 Controller                                  January 16, 2001
--------------------------          (Principal Financial and
Karen Schmedlin                     Accounting Officer)


--------------------------          Director                                    January   , 2001
Michel C. Bergerac


--------------------------          Director                                    January   , 2001
Frank T. Cary


/s/ James Ferguson                  Director                                    January 16, 2001
--------------------------
James Ferguson


/s/ Alan C. Sartorelli              Director                                    January 16, 2001
--------------------------
Alan C. Sartorelli

/s/ Walter B. Wriston
--------------------------          Director                                    January 16, 2001
Walter B. Wriston


--------------------------          Director                                    January   , 2001
Charles K. MacDonald
</TABLE>




<PAGE>



         INDEX TO EXHIBITS


<TABLE>
<CAPTION>
Exhibit
  No.    Description
-------  -------------------------------------------------------------------
<S>      <C>
4.1      Vion Pharmaceuticals, Inc.
         2000 Employee Stock Purchase Plan

5.1      Opinion of Fulbright & Jaworski L.L.P.

23.1     Consent of Ernst & Young LLP

23.2     Consent of Fulbright & Jaworski L.L.P. (included in Exhibit 5.1)

24.1     Power of Attorney (see signature page)
</TABLE>
[{"type": "S-8", "sequence": "1", "filename": "0001.txt", "description": "VION PHARMACEUTICALS, INC. S-8", "secsgml_size_bytes": 18001}]
{"company-data": {"conformed-name": "VION PHARMACEUTICALS INC", "cik": "0000944522", "assigned-sic": "2836", "irs-number": "133671221", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-53772", "film-number": "1509669"}, "business-address": {"street1": "4 SCIENCE PARK", "city": "NEW HAVEN", "state": "CT", "zip": "06511", "phone": "2034984210"}, "mail-address": {"street1": "FOUR SCIENCE PARK", "city": "NEW HAVEN", "state": "CT", "zip": "06511"}, "former-company": {"former-conformed-name": "ONCORX INC", "date-changed": "19950615"}}
As filed with the Securities and Exchange Commission on January 16, 2001
                                                   Registration No. 333-
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

                           VION PHARMACEUTICALS, INC.
             (Exact name of registrant as specified in its charter)

            DELAWARE                                       13-3671221
     (State or other juris-                             (I.R.S. Employer
    diction of incorporation                             Identification
         or organization)                                    Number)

                                 4 SCIENCE PARK
                          NEW HAVEN, CONNECTICUT 06511
                                 (203) 498-4210
          (Address, including zip code, and telephone number, including
            area code, of registrant's principal executive offices)

                           VION PHARMACEUTICALS, INC.
                        2000 EMPLOYEE STOCK PURCHASE PLAN
                            (full title of the plan)

                                  ALAN KESSMAN
                      PRESIDENT AND CHIEF EXECUTIVE OFFICER
                           VION PHARMACEUTICALS, INC.
                                 4 SCIENCE PARK
                          NEW HAVEN, CONNECTICUT 06511
                                 (203) 498-4210
            (Name, address, including zip code, and telephone number,
                   including area code, of agent for service)

       Copies of all communications, including all communications sent to
                   the agent for service, should be sent to:

                                PAUL JACOBS, ESQ.
                            LAWRENCE A. SPECTOR, ESQ.
                           FULBRIGHT & JAWORSKI L.L.P.
                                666 FIFTH AVENUE
                            NEW YORK, NEW YORK 10103
                                 (212) 318-3000

                         CALCULATION OF REGISTRATION FEE
----------------------------------------------------------------------------------------------------------------------------
TITLE OF SECURITIES TO BE        AMOUNT TO BE    PROPOSED MAXIMUM             PROPOSED MAXIMUM              AMOUNT OF
REGISTERED                       REGISTERED(1)   OFFERING PRICE PER UNIT      AGGREGATE OFFERING PRICE(2)   REGISTRATION FEE
----------------------------------------------------------------------------------------------------------------------------
COMMON STOCK $0.01 PAR VALUE
PER SHARE....................    450,000 SHARES  $7.836                       $3,526,200                    $881.55
============================================================================================================================
(1) Plus such additional indeterminable number of shares as may be required
pursuant to the Vion Pharmaceuticals, Inc. 2000 Employee Stock Purchase Plan in
the event of a stock dividend, stock split, recapitalization or other similar
change in the Common Stock.

(2) Computed in accordance with Rule 457(h) under the Securities Act of 1933, as
amended, such computation is based on $7.836 per share (85% of the average of
the high and the low prices of the registrant's common stock as reported on the
Nasdaq National Market on January 12, 2001). Pursuant to the Vion
Pharmaceuticals, Inc. Employee Stock Purchase Plan, shares are sold at 85% of
the lesser of the fair market value of such shares on the first day of an
offering period or the last day of the applicable purchase period.
PART I

                     INFORMATION REQUIRED IN THE PROSPECTUS

         In accordance with the rules and regulations of the Securities and
Exchange Commission (the "Commission"), the documents containing the information
called for in Part I of Form S-8 will be sent or given to individuals who
participate in the 2000 Employee Stock Purchase Plan adopted by Vion
Pharmaceuticals, Inc. (the "Company" or the "Registrant") and are not being
filed with or included in this Form S-8.
PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3.           INCORPORATION OF DOCUMENTS BY REFERENCE

                  The following documents filed by the Company are incorporated
herein by reference:

(i)   The Company's Annual Report on Form 10-KSB for the fiscal year ended
December 31, 1999.

(ii)  The Company's Quarterly Reports on Form 10-Q for the quarters ended March
31, 2000, June 30, 2000 and September 30, 2000.

(iii) The Company's Current Reports on Form 8-K filed on February 14, 2000,
March 28, 2000, June 22, 2000, November 8, 2000, November 13, 2000, December 1,
2000 and January 11, 2001.

(iv)  The Company's Proxy Statement on Schedule DEFR14A filed on September 19,
2000.

(v)   The description of the Company's Common Stock contained in Item 1 of the
Company's Registration Statement on Form 8-A filed July 31, 1995.

                  In addition to the foregoing, all documents subsequently filed
by the Company pursuant to Sections 13(a), 13(c), 14 and 15(d) of the Securities
Exchange Act of 1934, prior to the filing of a post-effective amendment
indicating that all of the securities offered hereunder have been sold or
deregistering all securities then remaining unsold, shall be deemed to be
incorporated by reference in this Registration Statement and to be part hereof
from the date of filing of such documents. Any statement contained in a document
incorporated by reference in this Registration Statement shall be deemed to be
modified or superseded for purposes of this Registration Statement to the extent
that a statement contained herein or in any subsequently filed document that is
also incorporated by reference herein modifies or supersedes such statement. Any
statement so modified or superseded shall not be deemed, except as so modified
or superseded, to constitute a part of this Registration Statement.

ITEM 4.           DESCRIPTION OF SECURITIES

                  Not applicable.

ITEM 5.           INTERESTS OF NAMED EXPERTS AND COUNSEL

                  Not applicable.

                                       2
ITEM 6.           INDEMNIFICATION OF DIRECTORS AND OFFICERS

                  Under the General Corporation Law of the State of Delaware
("DGCL"), a corporation may include provisions in its certificate of
incorporation that will relieve its directors of monetary liability for breaches
of their fiduciary duty to the corporation, except under certain circumstances,
including a breach of the director's duty of loyalty, acts or omissions of the
director not in good faith or which involve intentional misconduct or a knowing
violation of law, the approval of an improper payment of a dividend or an
improper purchase by the corporation of stock or any transaction from which the
director derived an improper personal benefit. The registrant's Restated
Certificate of Incorporation, as amended, eliminates the personal liability of
directors to the registrant or its stockholders for monetary damages for breach
of fiduciary duty as a director with certain limited exceptions set forth in the
DGCL.

                  Section 145 of the DGCL grants to corporations the power to
indemnify each officer and director against liabilities and expenses incurred by
reason of the fact that he or she is or was an officer or director of the
corporation if he or she acted in good faith and in a manner he or she
reasonably believed to be in or not opposed to the best interests of the
corporation and, with respect to any criminal action or proceeding, had no
reasonable cause to believe his or her conduct was unlawful. The registrant's
Restated Certificate of Incorporation, as amended, and Bylaws provide for
indemnification of each officer and director of the registrant to the fullest
extent permitted by the DGCL. Section 145 of the DGCL also empowers corporations
to purchase and maintain insurance on behalf of any person who is or was an
officer or director of the corporation against liability asserted against or
incurred by him in any such capacity, whether or not the corporation would have
the power to indemnify such officer or director against such liability under the
provisions of Section 145. The registrant has purchased and maintains a
directors' and officers' liability policy for such purposes.

ITEM 7.           EXEMPTION FROM REGISTRATION CLAIMED

                  Not Applicable.

ITEM 8.           EXHIBITS
4.1      --    Vion Pharmaceuticals, Inc. 2000 Employee Stock Purchase
                        Plan

         5.1      --    Opinion of Fulbright & Jaworski L.L.P.

         23.1     --    Consent of Ernst & Young LLP

         23.2     --    Consent of Fulbright & Jaworski L.L.P. (included in
                        Exhibit 5.1)

         24.1     --    Power of Attorney (included in signature page)

ITEM 9.           UNDERTAKINGS

         (a) The undersigned Registrant hereby undertakes:

                                       3
(1) To file, during any period in which offers or sales are
being made, a post-effective amendment to this Registration Statement:

                           (i)      To include any prospectus required by
section 10(a)(3) of the Securities Act of 1933;

                           (ii)     To reflect in the prospectus any facts or
events arising after the effective date of the registration statement (or the
most recent post-effective amendment thereof) which, individually or in the
aggregate, represent a fundamental change in the information set forth in the
registration statement. Notwithstanding the foregoing, any increase or decrease
in volume of securities offered (if the total dollar value of securities offered
would not exceed that which was registered) and any deviation from the low or
high end of the estimated maximum offering range may be reflected in the form of
prospectus filed with the Commission pursuant to Rule 424(b) if, in the
aggregate, the changes in volume and price represent no more than 20 percent
change in the maximum aggregate offering price set forth in the "Calculation of
Registration Fee" table in the effective registration statement;

                           (iii)    To include any material information with
respect to the plan of distribution not previously disclosed in the registration
statement or any material change to such information in the registration
statement;

                  (2) That, for the purpose of determining any liability under
the Securities Act of 1933, each such post-effective amendment shall be deemed
to be a new registration statement relating to the securities offered therein,
and the offering of such securities at that time shall be deemed to be the
initial bona fide offering thereof.

                  (3) To remove from registration by means of a post-effective
amendment any of the securities being registered which remain unsold at the
termination of the offering.

         (b) The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act of 1933, each filing of the
Registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Securities Exchange Act of 1934 (and, where applicable, each filing of an
employee benefit plan's annual report pursuant to Section 15(d) of the
Securities Exchange Act of 1934) that is incorporated by reference in the
registration statement shall be deemed to be a new registration statement
relating to the securities offered therein, and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.

         (c) Insofar as indemnification for liabilities arising under the
Securities Act of 1933 may be permitted to directors, officers and controlling
persons of the Registrant pursuant to the foregoing provisions, or otherwise,
the Registrant has been advised that in the opinion of the Securities and
Exchange Commission such indemnification is against public policy as expressed
in the Securities Act and is, therefore, unenforceable. In the event a claim for
indemnification against such liabilities (other than the payment by the
Registrant of expenses incurred or paid by a director, officer, or controlling
person of the Registrant in the successful defense of any action, suit or
proceeding) is asserted by such director, officer, or controlling person in
connection with

                                       4
the securities being registered hereunder, the Registrant will, unless in the
opinion of its counsel the matter has been settled by controlling precedent,
submit to a court of appropriate jurisdiction the question whether such
indemnification by it is against public policy as expressed in the Act and will
be governed by the final adjudication of such issue.

                                       5
SIGNATURES

                  Pursuant to the requirements of the Securities Act of 1933, as
amended, 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 Haven, State of Connecticut, on January 16,
2001.

                                        VION PHARMACEUTICALS, INC.

                                        By: /s/ Alan Kessman
                                           -------------------------------------
                                           Alan Kessman
                                           President and Chief Executive Officer

                                POWER OF ATTORNEY

                  KNOW ALL MEN BY THESE PRESENTS, that each person whose
signature appears below and on the following page constitutes and appoints Alan
Kessman and Karen Schmedlin as his true and lawful attorneys-in-fact and agents,
each acting alone, with full power of substitution and resubstitution, for him
and in his name, place and stead, in any and all capacities, to sign any and all
amendments to this Registration Statement, including post-effective amendments,
and to file the same, with all exhibits thereto, and all documents in connection
therewith, with the Securities and Exchange Commission, granting unto said
attorneys-in-fact and agents, and each of them, full power and authority of do
and perform each and every act and thing requisite and necessary to be done in
and about the premises, as fully to all intents and purposes as he might or
could do in person, and hereby ratifies and confirms all that said
attorneys-in-fact and agents, each acting alone, or their substitute or
substitutes, may lawfully do or cause to be done by virtue hereof.

                  Pursuant to the requirements of the Securities Act of 1933, as
amended, this registration statement has been signed below by the following
persons in the capacities and on the dates indicated.
Signature                                       Title                                Date
---------                                       -----                                ----
/s/ William R. Miller               Chairman of the Board                       January 16, 2001
--------------------------
William R. Miller

/s/ Alan Kessman                    President, Chief Executive                  January 16, 2001
--------------------------          Officer and Director (Principal
Alan Kessman                        Executive Officer)
/s/ Karen Schmedlin                 Controller                                  January 16, 2001
--------------------------          (Principal Financial and
Karen Schmedlin                     Accounting Officer)

--------------------------          Director                                    January   , 2001
Michel C. Bergerac

--------------------------          Director                                    January   , 2001
Frank T. Cary

/s/ James Ferguson                  Director                                    January 16, 2001
--------------------------
James Ferguson

/s/ Alan C. Sartorelli              Director                                    January 16, 2001
--------------------------
Alan C. Sartorelli

/s/ Walter B. Wriston
--------------------------          Director                                    January 16, 2001
Walter B. Wriston

--------------------------          Director                                    January   , 2001
Charles K. MacDonald
INDEX TO EXHIBITS
Exhibit
  No.    Description
-------  -------------------------------------------------------------------
4.1      Vion Pharmaceuticals, Inc.
         2000 Employee Stock Purchase Plan

5.1      Opinion of Fulbright & Jaworski L.L.P.

23.1     Consent of Ernst & Young LLP

23.2     Consent of Fulbright & Jaworski L.L.P. (included in Exhibit 5.1)

24.1     Power of Attorney (see signature page)