<Page>

   As filed with the Securities and Exchange Commission on September 14, 2001.

                                                     Registration No. 333-
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                  -------------

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

                                  -------------

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

      DELAWARE                                               13-3648318
      (State or other juris-                                 (I.R.S. Employer
      diction of incorporation                               Identification
      or organization)                                       Number)

                                352 KNOTTER DRIVE
                           CHESHIRE, CONNECTICUT 06410
                                 (203) 272-2596
    (Address, including zip code, and telephone number, including area code,
                  of registrant's principal executive offices)

                          ALEXION PHARMACEUTICALS, INC.
                             2000 STOCK OPTION PLAN

                                  -------------

                               LEONARD BELL, M.D.
                          ALEXION PHARMACEUTICALS, INC.
                                352 KNOTTER DRIVE
                           CHESHIRE, CONNECTICUT 06410
                                 (203) 272-2596

    (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:

                            MERRILL M. KRAINES, 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>
<S>                               <C>                            <C>                      <C>                         <C>
====================================================================================================================================
     TITLE OF SECURITIES                               PROPOSED MAXIMUM OFFERING   PROPOSED MAXIMUM AGGREGATE         AMOUNT OF
      TO BE REGISTERED        AMOUNT TO BE REGISTERED     PRICE PER UNIT(1)           OFFERING PRICE (1)          REGISTRATION FEE
====================================================================================================================================
COMMON STOCK, $0.0001 PAR
VALUE PER SHARE..............     1,500,000 SHARES               $17.88                   $26,820,000                 $6,705.00
</Table>

(1)   THE PRICE IS ESTIMATED IN ACCORDANCE WITH RULE 457(H)(1) UNDER THE
      SECURITIES ACT OF 1933, AS AMENDED, SOLELY FOR THE PURPOSE OF CALCULATING
      THE REGISTRATION FEE, BASED ON THE AVERAGE OF THE HIGH AND LOW PRICES OF
      THE COMMON STOCK AS REPORTED ON THE NASDAQ NATIONAL MARKET ON SEPTEMBER
      10, 2001.

<Page>

                                     PART I

              INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

ITEM 1.          DESCRIPTION OF PLAN.

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

ITEM 2.          REGISTRANT INFORMATION AND EMPLOYEE PLAN ANNUAL INFORMATION.

                 Upon written or oral request, Alexion Pharmaceuticals, Inc.
(the "Registrant") will provide without charge to participants in the 2000 Stock
Option Plan, the documents incorporated by reference in Item 3 of Part II of
this Registration Statement and the information required to be delivered to
employees pursuant to Rule 428(b). Requests should be directed to Thomas I. H.
Dubin, Esq., Vice President and General Counsel, Alexion Pharmaceuticals, Inc.,
352 Knotter Drive, Cheshire, CT 06410 (203/ 272-2596).

                                     PART II

             CAUTIONARY NOTICE REGARDING FORWARD-LOOKING STATEMENTS

                 Certain statements contained in, or incorporated by reference
in, this Registration Statement are forward-looking in nature. Such statements
can be identified by the use of forward-looking terminology, such as "believes,"
"expects," "may," "will," "should," or "anticipates," or the negative thereof or
comparable terminology, or by discussions of strategy. You are cautioned that
the Registrant's business and operations are subject to a variety of risks and
uncertainties and, consequently, its actual results may materially differ from
those projected by any forward-looking statements. Certain of such risks and
uncertainties are discussed below under the heading "Risk Factors." The
Registrant makes no commitment to revise or update any forward-looking
statements in order to reflect events or circumstances after the date any such
statement is made.

                       WHERE YOU CAN FIND MORE INFORMATION

                 The Registrant files reports, proxy statements, and other
information with the SEC. Such reports, proxy statements, and other information
can be read and copied at the SEC's Public Reference Room at 450 Fifth Street,
N.W., Washington, D.C. 20549. Please call the SEC at 1- 800-SEC-0330 for further
information on the Public Reference Room. The SEC maintains an Internet site at
HTTP://WWW.SEC.GOV that contains reports, proxy and information statements and
other information regarding issuers that file electronically with the SEC,
including the Registrant.

ITEM 3.          INCORPORATION OF DOCUMENTS BY REFERENCE.

                 The SEC allows the Registrant to "incorporate by reference" the
documents that it files with the SEC. This means that the Registrant can
disclose important information to you by referring you to those documents. Any
information incorporated in this manner is considered part of this Registration
Statement. Any information the Registrant files with SEC after the date of this
Registration Statement will automatically update and supersede the information
contained in this Registration Statement.

                 The Registrant incorporates by reference the following
documents that have been filed with the SEC and any filings that it will make
with the SEC in the future under Sections 13(a), 13(c), 14 or 15(d) of the
Securities Exchange Act of 1934 until the Registrant files a post-effective
amendment to this Registration Statement indicating this offering has been
completed:

(i)  our amended current report on Form 8-K/A, filed on November 20, 2000;

(ii) our current reports on Form 8-K, filed on September 25, 2000, October 3,
2000, October 27, 2000, January 23, 2001, January 29, 2001 and June 7, 2001;

(iii) our quarterly reports on Form 10-Q for the quarters ended October 31,
2000, January 31, 2001 and April 30, 2001, filed on December 15, 2000, March 15,
2001 and June 13, 2001, respectively;

(iv) our annual report on Form 10-K for the fiscal year ended July 31, 2000,
filed on October 6, 2000;

(v) our registration statement on Form 8-A, filed on February 21, 1997, as
amended on October 6, 2000; and

(vi) our registration statement on Form 8-A, filed on February 12, 1996.

ITEM 4.  DESCRIPTION OF SECURITIES.

                 Not applicable.


                                        2

<Page>

ITEM 5.  INTEREST OF NAMED EXPERTS AND COUNSEL.

                 Not applicable.


ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.

                 Section 145 of the Delaware General Corporation Law (the
"DGCL") empowers a Delaware corporation to indemnify any person who was or is a
party or is threatened to be made a party to any threatened, pending or
completed action, suit or proceeding, whether civil, criminal, administrative or
investigative (other than an action by or in the right of such corporation) by
reason of the fact that such person is or was a director, officer, employee or
agent of such corporation, or is or was serving at the request of such
corporation as a director, officer, employee or agent of another corporation or
enterprise. A corporation may, in advance of the final disposition of any civil,
criminal, administrative or investigative action, suit or proceeding, pay the
expenses (including attorneys' fees) incurred by any officer, director, employee
or agent in defending such action, provided that the director or officer
undertakes to repay such amount if it shall ultimately be determined that he is
not entitled to be indemnified by the corporation. A corporation may indemnify
such person against expenses (including attorneys' fees), judgments, fines and
amounts paid in settlement actually and reasonably incurred by such person in
connection with such action, suit or proceeding if he acted in good faith and in
a manner he 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 conduct was unlawful.

                 A Delaware corporation may indemnify officers and directors in
an action by or in the right of the corporation to procure a judgment in its
favor under the same conditions, except that no indemnification is permitted
without judicial approval if the officer or director is adjudged to be liable to
the corporation. Where an officer or director is successful on the merits or
otherwise in the defense of any action referred to above, the corporation must
indemnify him against the expenses (including attorneys fees) which he actually
and reasonably incurred in connection therewith. The indemnification provided is
not deemed to be exclusive of any other rights to which an officer or director
may be entitled under any corporation's by-law, agreement, vote or otherwise.

                 In accordance with Section 145 of the DGCL, Section EIGHTH of
the Company's Certificate of Incorporation, as amended (the "Certificate")
provides that the Company shall indemnify each person who is or was a director,
officer, employee or agent of the Company (including the heirs, executors,
administrators or estate of such person) or is or was serving at the request of
the Company as a director, officer, employee or agent of another corporation,
partnership, joint venture, trust or other enterprise, to the fullest extent
permitted. The indemnification provided by the Certificate shall not be deemed
exclusive of any other rights to which any of those seeking indemnification or
advancement of expenses may be entitled under any by-law, agreement, vote of
shareholders or disinterested directors or otherwise, both as to action in his
official capacity and as to action in another capacity while holding such
office, and shall continue as to a person who has ceased to be a director,
officer, employee or agent and shall inure to the benefit of the heirs,
executors and administrators of such a person. Expenses (including attorneys'
fees) incurred in defending a civil, criminal, administrative or investigative
action, suit or proceeding shall be paid by the Company in advance of the final
disposition of such action, suit or proceeding upon receipt of an undertaking by
or on behalf of the indemnified person to repay such amount if it shall
ultimately be determined that he is not entitled to be indemnified by the
company. Section NINTH of the certificate provides that a director of the
Company shall not be personally liable to the Company or its stockholders for
monetary damages for breach of fiduciary duty as a director, except for
liability (i) for any breach of the director's duty of loyalty to the Company or
its stockholders, (ii) for acts or omissions not in good faith or which involve
intentional misconduct or a knowing violation of law, (iii) under Section 174 of
the DGCL, or (iv) for any transaction from which the director derived an
improper personal benefit.

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

ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.

                 Not applicable.

ITEM 8.  EXHIBITS.

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

  4.1            Alexion Pharmaceuticals, Inc. 2000 Stock Option Plan

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

  23.1           Consent of Arthur Andersen LLP

  23.2           Consent of Arthur Andersen LLP

  23.3           Consent of Fulbright & Jaworski L.L.P. (Included in Exhibit 5)


                                        3

<Page>

  24.1           Power of Attorney (included on signature page)

ITEM 9.  UNDERTAKINGS.

                 (a)      The undersigned Registrant hereby undertakes:

                          (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;

                 PROVIDED, HOWEVER, that paragraphs (a) (1)(i) and (a)(1)(ii) do
not apply if the registration statement is on Form S-3, S-8 or Form F-3, and the
information required to be included in a post-effective amendment by those
paragraphs is contained in periodic reports filed by the Registrant pursuant to
Section 13 or Section 15(d) of the Securities Exchange Act of 1934 that are
incorporated by reference 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) The undersigned Registrant hereby undertakes to deliver or
cause to be delivered with the prospectus, to each person to whom the prospectus
is sent or given, the latest annual report to securityholders that is
incorporated by reference in the prospectus and furnished pursuant to and
meeting the requirements of Rule 14a-3 or Rule 14c-3 under the Securities
Exchange Act of 1934; and, the interim financial information required to be
presented by Article 3 of Regulation S-X is not set forth in the prospectus, to
deliver, or cause to be delivered to each person to whom the prospectus is sent
or given, the latest quarterly report that is specifically incorporated by
reference in the prospectus to provide such interim financial information.

                 (d) 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 Act and is, therefore, unenforceable. In the event that 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 the securities being registered, 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.

                 (e)      The undersigned Registrant hereby undertakes that:

                          (1) For purposes of determining any liability under
the Securities Act of 1933, the information omitted from the form of prospectus
filed as part of this registration statement in reliance upon Rule 430A and
contained in a form of prospectus filed by the Registrant pursuant to Rule
424(b)(1) or (4) or 497(h) under the Securities Act shall be deemed to be part
of this registration statement as of the time it was declared effective.

                          (2) For the purpose of determining any liability under
the Securities Act of 1933, each post-effective amendment that


                                       4
<Page>

contains a form of prospectus 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.

                 (f)      The undersigned Registrant hereby undertakes that:

                          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 Act and is, therefore, unenforceable. In the event that 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 the securities being registered, 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 Town of Cheshire, State of Connecticut on September 14,
2001.

                                   ALEXION PHARMACEUTICALS, INC.


                                   By: /s/ LEONARD BELL
                                       -----------------------------------------
                                       Leonard Bell, M.D.
                                       President, Chief Executive Officer,
                                       Secretary and Treasurer


                                        6

<Page>



                                POWER OF ATTORNEY

                 KNOW ALL MEN BY THESE PRESENTS, that each individual whose
signature appears below constitutes and appoints LEONARD BELL, M.D. and DAVID W.
KEISER, or either of them, his true and lawful attorney-in-fact and agent 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 statements (including
post-effective amendments) to this Registration Statement and to file the same
with all exhibits thereto and all documents in connection therewith, with the
Securities and Exchange Commission, granting said attorney-in-fact and agent and
each of them, full power and authority to 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 or she might or could do in person, hereby
ratifying and confirming all that said attorney-in-fact and agent or any of
them, or their or his 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>
<S>                                <C>                                              <C>

/s/ LEONARD BELL                   Chief Executive Officer, Secretary, Treasurer    September 14, 2001
--------------------------         and Director
Leonard Bell                       (principal executive officer)


/s/ DAVID W. KEISER                Executive Vice President and Chief Operating     September 14, 2001
--------------------------         Officer
David W. Keiser                    (principal financial officer)


            *                      Vice President of Finance and Administration     September 14, 2001
--------------------------         (principal accounting officer)
Barry P. Luke

            *                      Chairman of the Board of Directors               September 14, 2001
--------------------------
John H. Fried

            *                      Director                                         September 14, 2001
--------------------------
Jerry T. Jackson

            *                      Director                                         September 14, 2001
--------------------------
Max Link

            *                      Director                                         September 14, 2001
--------------------------
Joseph A. Madri

            *                      Director                                         September 14, 2001
--------------------------
R. Douglas Norby

            *                      Director                                         September 14, 2001
--------------------------
Alvin S. Parven
</Table>




*By: /s/ Leonard Bell
     -----------------------------------------
         Leonard Bell


                                       7
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{"company-data": {"conformed-name": "ALEXION PHARMACEUTICALS INC", "cik": "0000899866", "assigned-sic": "2834", "irs-number": "133648318", "state-of-incorporation": "DE", "fiscal-year-end": "0731"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-69478", "film-number": "1738443"}, "business-address": {"street1": "352 KNOTTER DRIVE", "city": "CHESHIRE", "state": "CT", "zip": "06511", "phone": "2037761790"}, "mail-address": {"street1": "352 KNOTTER DRIVE", "city": "CHESHIRE", "state": "CT", "zip": "06511"}}
As filed with the Securities and Exchange Commission on September 14, 2001.

                                                     Registration No. 333-
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                  -------------

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

                                  -------------

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

      DELAWARE                                               13-3648318
      (State or other juris-                                 (I.R.S. Employer
      diction of incorporation                               Identification
      or organization)                                       Number)

                                352 KNOTTER DRIVE
                           CHESHIRE, CONNECTICUT 06410
                                 (203) 272-2596
    (Address, including zip code, and telephone number, including area code,
                  of registrant's principal executive offices)

                          ALEXION PHARMACEUTICALS, INC.
                             2000 STOCK OPTION PLAN

                                  -------------

                               LEONARD BELL, M.D.
                          ALEXION PHARMACEUTICALS, INC.
                                352 KNOTTER DRIVE
                           CHESHIRE, CONNECTICUT 06410
                                 (203) 272-2596

    (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:

                            MERRILL M. KRAINES, 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                               PROPOSED MAXIMUM OFFERING   PROPOSED MAXIMUM AGGREGATE         AMOUNT OF
      TO BE REGISTERED        AMOUNT TO BE REGISTERED     PRICE PER UNIT(1)           OFFERING PRICE (1)          REGISTRATION FEE
====================================================================================================================================
COMMON STOCK, $0.0001 PAR
VALUE PER SHARE..............     1,500,000 SHARES               $17.88                   $26,820,000                 $6,705.00
(1)   THE PRICE IS ESTIMATED IN ACCORDANCE WITH RULE 457(H)(1) UNDER THE
      SECURITIES ACT OF 1933, AS AMENDED, SOLELY FOR THE PURPOSE OF CALCULATING
      THE REGISTRATION FEE, BASED ON THE AVERAGE OF THE HIGH AND LOW PRICES OF
      THE COMMON STOCK AS REPORTED ON THE NASDAQ NATIONAL MARKET ON SEPTEMBER
      10, 2001.
PART I

              INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

ITEM 1.          DESCRIPTION OF PLAN.

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

ITEM 2.          REGISTRANT INFORMATION AND EMPLOYEE PLAN ANNUAL INFORMATION.

                 Upon written or oral request, Alexion Pharmaceuticals, Inc.
(the "Registrant") will provide without charge to participants in the 2000 Stock
Option Plan, the documents incorporated by reference in Item 3 of Part II of
this Registration Statement and the information required to be delivered to
employees pursuant to Rule 428(b). Requests should be directed to Thomas I. H.
Dubin, Esq., Vice President and General Counsel, Alexion Pharmaceuticals, Inc.,
352 Knotter Drive, Cheshire, CT 06410 (203/ 272-2596).

                                     PART II

             CAUTIONARY NOTICE REGARDING FORWARD-LOOKING STATEMENTS

                 Certain statements contained in, or incorporated by reference
in, this Registration Statement are forward-looking in nature. Such statements
can be identified by the use of forward-looking terminology, such as "believes,"
"expects," "may," "will," "should," or "anticipates," or the negative thereof or
comparable terminology, or by discussions of strategy. You are cautioned that
the Registrant's business and operations are subject to a variety of risks and
uncertainties and, consequently, its actual results may materially differ from
those projected by any forward-looking statements. Certain of such risks and
uncertainties are discussed below under the heading "Risk Factors." The
Registrant makes no commitment to revise or update any forward-looking
statements in order to reflect events or circumstances after the date any such
statement is made.

                       WHERE YOU CAN FIND MORE INFORMATION

                 The Registrant files reports, proxy statements, and other
information with the SEC. Such reports, proxy statements, and other information
can be read and copied at the SEC's Public Reference Room at 450 Fifth Street,
N.W., Washington, D.C. 20549. Please call the SEC at 1- 800-SEC-0330 for further
information on the Public Reference Room. The SEC maintains an Internet site at
HTTP://WWW.SEC.GOV that contains reports, proxy and information statements and
other information regarding issuers that file electronically with the SEC,
including the Registrant.

ITEM 3.          INCORPORATION OF DOCUMENTS BY REFERENCE.

                 The SEC allows the Registrant to "incorporate by reference" the
documents that it files with the SEC. This means that the Registrant can
disclose important information to you by referring you to those documents. Any
information incorporated in this manner is considered part of this Registration
Statement. Any information the Registrant files with SEC after the date of this
Registration Statement will automatically update and supersede the information
contained in this Registration Statement.

                 The Registrant incorporates by reference the following
documents that have been filed with the SEC and any filings that it will make
with the SEC in the future under Sections 13(a), 13(c), 14 or 15(d) of the
Securities Exchange Act of 1934 until the Registrant files a post-effective
amendment to this Registration Statement indicating this offering has been
completed:

(i)  our amended current report on Form 8-K/A, filed on November 20, 2000;

(ii) our current reports on Form 8-K, filed on September 25, 2000, October 3,
2000, October 27, 2000, January 23, 2001, January 29, 2001 and June 7, 2001;

(iii) our quarterly reports on Form 10-Q for the quarters ended October 31,
2000, January 31, 2001 and April 30, 2001, filed on December 15, 2000, March 15,
2001 and June 13, 2001, respectively;

(iv) our annual report on Form 10-K for the fiscal year ended July 31, 2000,
filed on October 6, 2000;

(v) our registration statement on Form 8-A, filed on February 21, 1997, as
amended on October 6, 2000; and

(vi) our registration statement on Form 8-A, filed on February 12, 1996.

ITEM 4.  DESCRIPTION OF SECURITIES.

                 Not applicable.

                                        2
ITEM 5.  INTEREST OF NAMED EXPERTS AND COUNSEL.

                 Not applicable.

ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.

                 Section 145 of the Delaware General Corporation Law (the
"DGCL") empowers a Delaware corporation to indemnify any person who was or is a
party or is threatened to be made a party to any threatened, pending or
completed action, suit or proceeding, whether civil, criminal, administrative or
investigative (other than an action by or in the right of such corporation) by
reason of the fact that such person is or was a director, officer, employee or
agent of such corporation, or is or was serving at the request of such
corporation as a director, officer, employee or agent of another corporation or
enterprise. A corporation may, in advance of the final disposition of any civil,
criminal, administrative or investigative action, suit or proceeding, pay the
expenses (including attorneys' fees) incurred by any officer, director, employee
or agent in defending such action, provided that the director or officer
undertakes to repay such amount if it shall ultimately be determined that he is
not entitled to be indemnified by the corporation. A corporation may indemnify
such person against expenses (including attorneys' fees), judgments, fines and
amounts paid in settlement actually and reasonably incurred by such person in
connection with such action, suit or proceeding if he acted in good faith and in
a manner he 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 conduct was unlawful.

                 A Delaware corporation may indemnify officers and directors in
an action by or in the right of the corporation to procure a judgment in its
favor under the same conditions, except that no indemnification is permitted
without judicial approval if the officer or director is adjudged to be liable to
the corporation. Where an officer or director is successful on the merits or
otherwise in the defense of any action referred to above, the corporation must
indemnify him against the expenses (including attorneys fees) which he actually
and reasonably incurred in connection therewith. The indemnification provided is
not deemed to be exclusive of any other rights to which an officer or director
may be entitled under any corporation's by-law, agreement, vote or otherwise.

                 In accordance with Section 145 of the DGCL, Section EIGHTH of
the Company's Certificate of Incorporation, as amended (the "Certificate")
provides that the Company shall indemnify each person who is or was a director,
officer, employee or agent of the Company (including the heirs, executors,
administrators or estate of such person) or is or was serving at the request of
the Company as a director, officer, employee or agent of another corporation,
partnership, joint venture, trust or other enterprise, to the fullest extent
permitted. The indemnification provided by the Certificate shall not be deemed
exclusive of any other rights to which any of those seeking indemnification or
advancement of expenses may be entitled under any by-law, agreement, vote of
shareholders or disinterested directors or otherwise, both as to action in his
official capacity and as to action in another capacity while holding such
office, and shall continue as to a person who has ceased to be a director,
officer, employee or agent and shall inure to the benefit of the heirs,
executors and administrators of such a person. Expenses (including attorneys'
fees) incurred in defending a civil, criminal, administrative or investigative
action, suit or proceeding shall be paid by the Company in advance of the final
disposition of such action, suit or proceeding upon receipt of an undertaking by
or on behalf of the indemnified person to repay such amount if it shall
ultimately be determined that he is not entitled to be indemnified by the
company. Section NINTH of the certificate provides that a director of the
Company shall not be personally liable to the Company or its stockholders for
monetary damages for breach of fiduciary duty as a director, except for
liability (i) for any breach of the director's duty of loyalty to the Company or
its stockholders, (ii) for acts or omissions not in good faith or which involve
intentional misconduct or a knowing violation of law, (iii) under Section 174 of
the DGCL, or (iv) for any transaction from which the director derived an
improper personal benefit.

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

ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.

                 Not applicable.

ITEM 8.  EXHIBITS.

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

  4.1            Alexion Pharmaceuticals, Inc. 2000 Stock Option Plan

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

  23.1           Consent of Arthur Andersen LLP

  23.2           Consent of Arthur Andersen LLP

  23.3           Consent of Fulbright & Jaworski L.L.P. (Included in Exhibit 5)

                                        3
24.1           Power of Attorney (included on signature page)

ITEM 9.  UNDERTAKINGS.

                 (a)      The undersigned Registrant hereby undertakes:

                          (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;

                 PROVIDED, HOWEVER, that paragraphs (a) (1)(i) and (a)(1)(ii) do
not apply if the registration statement is on Form S-3, S-8 or Form F-3, and the
information required to be included in a post-effective amendment by those
paragraphs is contained in periodic reports filed by the Registrant pursuant to
Section 13 or Section 15(d) of the Securities Exchange Act of 1934 that are
incorporated by reference 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) The undersigned Registrant hereby undertakes to deliver or
cause to be delivered with the prospectus, to each person to whom the prospectus
is sent or given, the latest annual report to securityholders that is
incorporated by reference in the prospectus and furnished pursuant to and
meeting the requirements of Rule 14a-3 or Rule 14c-3 under the Securities
Exchange Act of 1934; and, the interim financial information required to be
presented by Article 3 of Regulation S-X is not set forth in the prospectus, to
deliver, or cause to be delivered to each person to whom the prospectus is sent
or given, the latest quarterly report that is specifically incorporated by
reference in the prospectus to provide such interim financial information.

                 (d) 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 Act and is, therefore, unenforceable. In the event that 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 the securities being registered, 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.

                 (e)      The undersigned Registrant hereby undertakes that:

                          (1) For purposes of determining any liability under
the Securities Act of 1933, the information omitted from the form of prospectus
filed as part of this registration statement in reliance upon Rule 430A and
contained in a form of prospectus filed by the Registrant pursuant to Rule
424(b)(1) or (4) or 497(h) under the Securities Act shall be deemed to be part
of this registration statement as of the time it was declared effective.

                          (2) For the purpose of determining any liability under
the Securities Act of 1933, each post-effective amendment that

                                       4
contains a form of prospectus 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.

                 (f)      The undersigned Registrant hereby undertakes that:

                          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 Act and is, therefore, unenforceable. In the event that 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 the securities being registered, 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 Town of Cheshire, State of Connecticut on September 14,
2001.

                                   ALEXION PHARMACEUTICALS, INC.

                                   By: /s/ LEONARD BELL
                                       -----------------------------------------
                                       Leonard Bell, M.D.
                                       President, Chief Executive Officer,
                                       Secretary and Treasurer

                                        6
POWER OF ATTORNEY

                 KNOW ALL MEN BY THESE PRESENTS, that each individual whose
signature appears below constitutes and appoints LEONARD BELL, M.D. and DAVID W.
KEISER, or either of them, his true and lawful attorney-in-fact and agent 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 statements (including
post-effective amendments) to this Registration Statement and to file the same
with all exhibits thereto and all documents in connection therewith, with the
Securities and Exchange Commission, granting said attorney-in-fact and agent and
each of them, full power and authority to 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 or she might or could do in person, hereby
ratifying and confirming all that said attorney-in-fact and agent or any of
them, or their or his 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.
/s/ LEONARD BELL                   Chief Executive Officer, Secretary, Treasurer    September 14, 2001
--------------------------         and Director
Leonard Bell                       (principal executive officer)

/s/ DAVID W. KEISER                Executive Vice President and Chief Operating     September 14, 2001
--------------------------         Officer
David W. Keiser                    (principal financial officer)

            *                      Vice President of Finance and Administration     September 14, 2001
--------------------------         (principal accounting officer)
Barry P. Luke

            *                      Chairman of the Board of Directors               September 14, 2001
--------------------------
John H. Fried

            *                      Director                                         September 14, 2001
--------------------------
Jerry T. Jackson

            *                      Director                                         September 14, 2001
--------------------------
Max Link

            *                      Director                                         September 14, 2001
--------------------------
Joseph A. Madri

            *                      Director                                         September 14, 2001
--------------------------
R. Douglas Norby

            *                      Director                                         September 14, 2001
--------------------------
Alvin S. Parven
*By: /s/ Leonard Bell
     -----------------------------------------
         Leonard Bell

                                       7