AMENDMENT

                                                               [EXHIBIT 99.3.1]


                                 AMENDMENT


      AMENDMENT, dated as of May 27, 1997 (this "Amendment"), to the
International Collaboration Agreement, effective as of June 28, 1996 (the
"Agreement") by and between Xxxxxx-Xxxxxxx Company, a Delaware corporation
("Xxxxxx-Xxxxxxx"), and Pfizer Inc., a Delaware corporation ("Pfizer").
Capitalized terms not otherwise defined herein have the meanings set forth
in the Agreement.

      WHEREAS, Xxxxxx-Xxxxxxx has assigned certain of its rights and
obligations under the Agreement to Xxxxxx-Xxxxxxx Export Limited, a company
organized and existing under the laws of Ireland ("Export"), in accordance
with the Assignment and Assumption Agreement dated as of November 1, 1996;
and

      WHEREAS, Pfizer has assigned certain of its rights and obligations
under the Agreement to Pfizer Overseas Inc., a corporation organized and
existing under the laws of Delaware ("Pfizer Overseas"); and

      WHEREAS, upon this Amendment becoming effective, the parties have
agreed that certain provisions of the Agreement be amended in the manner
provided for in this Amendment;

      NOW, THEREFORE, the parties hereto hereby agree as follows:

                           ARTICLE I - AMENDMENTS

      Section 1.01  Amendments of Section 1.01.

      (a) The definition of "Co-Promotion Territory" in Section 1.01 of the
Agreement is hereby amended by deleting from the second line thereof the
country "Greece,".

      (b) The definition of "License Territory" in Section 1.01 of the
Agreement is hereby amended by inserting the countries "Egypt, Greece," in
the second line thereof before the country "Iceland."

      Section 1.02  Amendment of Section 3.05(a). Section 3.05(a) is hereby
amended by inserting the following phrase after the words "Net Sales" in
the tenth line thereof: "or, to the extent that XXXXXX-XXXXXXX packages the
Products for PFIZER 30% of Net Sales,".


                         ARTICLE II - MISCELLANEOUS

      Section 2.01  No Other Amendments; Confirmation. Except as expressly
amended, waived, modified and supplemented hereby, the provisions of the
Agreement are and shall remain in full force and effect.

      Section 2.02  Governing Law. This Amendment shall be governed by and
construed in accordance with the law of the State of New York other than
those provisions governing conflicts of law.

      Section 2.03  Headings. The headings used in this Amendment have been
inserted for convenience of reference only and do not define or limit the
provisions hereof.

      Section 2.04  Third Party Beneficiaries. None of the provisions of this
Amendment shall be for the benefit of or enforceable by any third party,
including, without limitation, any creditor of either party hereto. No such
third party shall obtain any right under any provision of this Amendment or
shall by reason of any such provision make any claim in respect of any
debt, liability or obligation (or otherwise) against either party hereto.

      IN WITNESS WHEREOF, the parties hereto, by their duly authorized
officers, have executed this Amendment as of the date first
written above.


XXXXXX-XXXXXXX                            PFIZER OVERSEAS INC.
EXPORT LIMITED



By:/s/ Xxxx X. Xxxxx                      By:/s/ Xxxxxx X. Xxxxxx
   -------------------------                 ----------------------------
   Name:  Xxxx X. Xxxxx                      Name:  Xxxxxx X. Xxxxxx
   Title: Managing Director                  Title: Vice President