SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549

                               Amendment No. 1 to
                                    Form 8-A

                FOR REGISTRATION OF CERTAIN CLASSES OF SECURITIES
                     PURSUANT TO SECTION 12(b) OR (g) OF THE
                         SECURITIES EXCHANGE ACT OF 1934

                          Alexion Pharmaceuticals, Inc.
                          -----------------------------
             (Exact name of registrant as specified in its charter)

                Delaware                                  13-3648318
                --------                                  ----------
(State of incorporation or organization)       (IRS Employer Identification No.)

25 Science Park, New Haven, Connecticut                      06511
- ---------------------------------------                      -----
(Address of principal executive offices)                   (Zip Code)

Securities to be registered pursuant to Section 12(b) of the Act:

           Title of each class                       Name of each exchange
           to be so registered                       on which each class is
                                                     to be registered

                   None                                       None
           -------------------                       ----------------------

Securities to be registered pursuant to Section 12(g) of the Act:

          Rights to Purchase Junior Participating Cumulative Preferred
               Stock, $1.00 par value per share, of the Registrant
               ---------------------------------------------------
                                (Title of Class)

ITEM 1. DESCRIPTION OF REGISTRANT'S SECURITIES TO BE REGISTERED On February 14, 1997 the Board of Directors of the Registrant declared a dividend of one preferred stock purchase right (a "Right") for each outstanding share of Common Stock, par value $.0001 per share (the "Common Stock") of the Registrant. The Rights were issued to the stockholders of record on March 6, 1997 and will expire in ten years, subject to earlier redemption. Under certain circumstances, each Right entitles the registered holder to purchase from the Registrant one one-hundredth of a share of Junior Participating Cumulative Preferred Stock, par value $1.00 per share ("Preferred Stock"), of the Registrant or, in certain circumstances, either Common Stock or common stock of an acquiring company at one-half the market price of such Common Stock or common stock, as the case may be. The Rights were designed to make it more likely that all the Registrant's stockholders receive fair and equal treatment in the event of any proposed takeover of the Registrant and to guard against the use of partial tender offers or other coercive tactics to gain control of the Registrant. The description and terms of the Rights are set forth in a Rights Agreement (the "Rights Agreement") between the Registrant and Continental Stock Transfer & Trust Company, as Rights Agent (the "Rights Agent"). Exercise Price On September 18, 2000, the Board of Directors of Registrant amended the purchase price under Registrant's Shareholder Rights Plan. Such purchase price, for each one one-hundredth of a share of Preferred Stock to be issued upon the exercise of each Right under the Rights Agreement was increased from $75.00 to $725.00. Except for the increase in the purchase price, the terms and conditions of the Rights remain unchanged from the description contained in the Form 8-A filed on February 21, 1997. A copy of Amendment No. 1 to the Rights Agreement is attached hereto as Exhibit 10.1 and is incorporated herein by reference. The foregoing description of the amendment to the Rights is qualified in its entirety by reference to such Exhibit.

ITEM 2. EXHIBITS 1. Amendment No. 1 to Rights Agreement, dated as of September 18, 2000, between the Registrant and Continental Stock Transfer and Trust Company.

SIGNATURE Pursuant to the requirements of Section 12 of the Securities Exchange Act of 1934, the Registrant has duly caused this Registration Statement to be signed on its behalf by the undersigned thereto duly authorized. ALEXION PHARMACEUTICALS, INC. (Registrant) By /s/ Leonard Bell -------------------------- Leonard Bell President DATE: October 6, 2000

EXHIBIT INDEX Sequential Exhibit No. Description Page No. - ----------- ----------- -------- 10.1 Amendment No. 1 to Rights Agreement, dated as of September 18, 2000, between the Registrant and Continental Stock Transfer and Trust Company.


                                                                    Exhibit 10.1

                               AMENDMENT NO. 1 TO
                                RIGHTS AGREEMENT

            This AMENDMENT NO. 1 RIGHTS AGREEMENT (the "Amendment") is made as
of September 18, 2000 between Alexion Pharmaceuticals, Inc., a Delaware
corporation (the "Company"), and Continental Stock Transfer & Trust Company, a
New York corporation (the "Rights Agent").

            WHEREAS, on February 14, 1997, the Board of Directors of the Company
declared a dividend of one preferred stock purchase right ("Right") for each
share of Common Stock, par value $.0001 per share, of the Company outstanding at
the close of business on March 6, 1997; and

            WHEREAS, each Right entitles the registered holder thereof to
purchase from the Company one one-hundreth (1/100 th) of a share of Junior
Participating Cumulative Preferred Stock, par value $1.00 per share, of the
Company or, in certain circumstances, either Common Stock of the Company or
common stock of an aquiring company at one-half the market price of the Common
Stock of the Company; and

            WHEREAS, the description and terms of the Rights are set forth in a
Rights Agreement (the "Rights Agreement") between the Company and the Rights
Agent; and

            WHEREAS, the Purchase Price per each one one-hundreth of a share of
Preferred Stock payable upon the exercise o f a Right is set forth in the Rights
Agreement; and

            WHEREAS, in view of the increase in the value of the Common Stock of
the Company, the Company desires to amend the Rights Agreement in order to
provide for an increase in the Purchase Price; and

            WHEREAS, the Stock Acquisition Date referred to in the Rights
Agreement has not occurred;

NOW, THEREFORE, in consideration of the premises and the agreements set forth herein, the parties hereby agree as follows: 1. Purchase Price Increase. Section 7(b) of the Agreement is hereby amended in its entirety to read as follows: "(b) The Purchase Price for each one one-hundreth of a share of Preferred Stock issued pursuant to the exercise of a Right shall initially be $725.00, shall be subject to adjustment from time to time as provided in Sections 11 and 13 hereof and shall be payable in lawful money of the United States of America in accordance with paragraph (c) below." 2. No Further Amendment. Except as expressly amended by this Amendment No. 1, the Rights Agreement shall remain in full force and effect as the same was in effect immediately prior to the date of this Amendment No. 1. 3. Counterparts. This Amendment may be executed in any number of counterparts and each of such counterparts shall for all purposes be deemed to be an original, and all such counterparts shall together constitute but one and the same instrument. IN WITNESS WHEREOF, the undersigned have duly executed this Amendment as of the date first above written. ATTEST: ALEXION PHARMACEUTICALS, INC. By: /s/David Keiser By: /s/ Leonard Bell ------------------------------- ------------------------------- Name:David Keiser Name: Leonard Bell Title:Chief Financial Officer Title:President ATTEST: CONTINENTAL STOCK TRANSFER & TRUST COMPANY By: /s/ Thomas Jennings By: /s/ William F. Seegraber ------------------------------- ------------------------------- Name: Thomas Jennings Name: William F. Seegraber Title: Asst. Secretary Title: Vice President