AMENDMENT NO. 2
                             to AMENDED AND RESTATED
                              GOVERNANCE AGREEMENT

     This  Amendment No. 2  ("Amendment  No. 2") is made this 9th day of August,
2000 (the "Amendment  Effective Date") by and between AMERICAN CYANAMID COMPANY,
a  corporation  organized  and  existing  under  the laws of the  State of Maine
("CYANAMID")   and  a   wholly-owned   subsidiary   of  AMERICAN  HOME  PRODUCTS
CORPORATION, a corporation organized and existing under the laws of the State of
Delaware and having its principal  office at Five Giralda  Farms,  Madison,  New
Jersey 07940  ("AHPC") and IMMUNEX  CORPORATION,  a  corporation  organized  and
existing  under the laws of the State of  Washington  and having  its  principal
office at 51 University Street, Seattle,  Washington 98101 ("IMMUNEX"),  further
amends the Amended and Restated  Governance  Agreement  dated as of December 15,
1992, among American Cyanamid Company,  Immunex Corporation and Lederle Oncology
Corporation as amended by Amendment No. 1 to the Governance Agreement, dated May
20, 1999 (as amended, the "Governance Agreement").

     WHEREAS,  AHPC and IMMUNEX  have  entered  into a Letter  Agreement,  dated
August 9, 2000,  under which AHPC requested and IMMUNEX agreed to file and filed
a shelf  registration  statement  on Form S-3 with the  Securities  and Exchange
Commission  on August 9, 2000  covering  the  proposed  sale of up to 20 million
shares  of  newly  issued  Common  Stock in a  primary  offering  (the  "Primary
Offering") and up to 50 million  shares of Common Stock in a secondary  offering
(the  "Secondary   Offering"  and  together  with  the  Primary  Offering,   the
"Offering");

     WHEREAS,  AHPC and IMMUNEX  have agreed to make certain  amendments  to the
Governance Agreement effective upon the closing of a Secondary Offering upon the
completion of which Cyanamid's Interest is below 45%;

     NOW THEREFORE,  in consideration of the mutual covenants  contained herein,
and for other good and valuable  consideration,  the receipt and  sufficiency of
which are hereby acknowledged,  the parties hereto, each intending to be legally
bound, hereby agree as follows:

     1. All initially  capitalized  terms used herein and not defined shall have
the meanings set forth in the Governance Agreement.

     2. Effective  upon the closing of a Secondary  Offering upon the completion
of which Cyanamid's Interest is below 45%:

     (a)         Notwithstanding  anything  in  Section  4.01 (b) and (c) of the
                 Governance Agreement to the contrary, at all times during which
                 AHPC  has the  right to  designate  no more  than two  Investor
                 Directors,  IMMUNEX  shall  have the right to  designate  three
                 Management   Directors   and  there  shall  be  at  least  four
                 Independent Directors.

     (b)         For  the  duration  of any  lock up  period  under  the  letter
                 agreement  between  AHP  and  IMMUNEX  dated  August  9,  2000,
                 notwithstanding  anything  to the  contrary  in the  Governance
                 Agreement,  for  purposes  of  determining  whether  Cyanamid's
                 Interest  is below 35% no  consideration  shall be given to any
                 shares of  IMMUNEX  Common  Stock  issued  during  each lock up
                 period as a result of the  exercise of any employee or director
                 stock options.

     (c)         Section 4.04 of the Governance Agreement will be amended as
                 follows:

                 (i)    Section 4.04(g) shall be deleted in its entirety;

                 (ii)   Each of Sections 4.04(h), (i) and (j) shall be amended
                        to delete the amount "$350,000" and substitute in its
                        place the amount "$15 million";

                  (iii) Section 4.04(l) shall be amended to delete the
                        subsection in its entirety and substitute the following:

                         "(l)  the  acquisition  by  the  Company  or any of its
                         Subsidiaries   of  technology  or  products  under  any
                         license or  similar  arrangements  unless the  purchase
                         price or the fair market  value of such  technology  or
                         products (determined in accordance with Title II of the
                         Hart-Scott-Rodino  Antitrust  Improvements Act of 1976,
                         as amended  and the rules and  regulations  promulgated
                         thereunder) is less than $15 million;

     3. Except as otherwise  set forth in this  Amendment No. 2 or Amendment No.
1, all other terms and  provisions of the Governance  Agreement  shall remain in
full force and effect.

     4. This  Amendment  No. 2 may be  executed in  counterparts,  each of which
shall be deemed an original and all of which shall  constitute  together one and
the same instrument.

     IN WITNESS  WHEREOF,  the parties hereto have executed this Amendment No. 2
as of the day and year first above written.

                                           IMMUNEX CORPORATION

                                           By:/s/ Edward V. Fritzky
                                              Edward V. Fritzky
                                              Chairman and Chief
                                              Executive Officer

                                           AMERICAN CYANAMID COMPANY

                                           By:/s/ Jeffrey S. Sherman
                                           Name:  Jeffrey S. Sherman
                                           Title: Vice President

                                           AMERICAN HOME PRODUCTS CORPORATION

                                           By:/s/ Kenneth J. Martin
                                           Name:  Kenneth J. Martin
                                           Title: Senior Vice President and
                                                  Chief Financial Officer