1
CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY BRACKETS,
HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE
COMMISSION PURSUANT TO RULE 24B-2 OF THE SECURITIES EXCHANGE ACT OF 1934, AS
AMENDED.


                                                                  EXHIBIT 10.124

                          FOURTH AMENDMENT TO AGREEMENT

        This is the fourth amendment to the Research Collaboration and License
Agreement between MERCK & CO., INC., a corporation organized and existing under
the laws of New Jersey ("MERCK") and ARRIS PHARMACEUTICAL CORPORATION, a
corporation organized and existing under the laws of Delaware, now known as Axys
Pharmaceuticals, Inc. ("AXYS") made as of November 6, 1996 (the "Agreement").
The purpose of this fourth amendment is to increase the number of FTEs for the
period March 5, 2000 through November 5, 2000.

        1. In accordance with the provisions of Section 2.8 and Section 5.2(d)
of the Agreement and subject to MERCK's right to terminate the Research Program
and the Agreement in accordance with Section 8.2, the parties agree that [ * ]
FTE's will be required during the period March 5, 2000 through November 5, 2000
payable at an annual rate of [ * ] per FTE.

        2. Capitalized terms used and not otherwise defined herein shall have
the respective meanings set forth in the Agreement. The Agreement, together with
the first amendment dated November 18, 1999, and this fourth amendment contain
the entire understanding of the parties with respect to their subject matter.
All express or implied agreements and understandings, either oral or written,
heretofore made are expressly merged in and made a part of the Agreement as
amended by the first, second, third and fourth amendments. All other terms and
conditions of the Agreement, as amended, continue in full force and effect. The
Agreement and its amendments may be amended, or any term thereof modified, only
by a written instrument duly executed by both parties hereto.

        IN WITNESS WHEREOF, the parties have entered into this Amendment as of
March 3, 2000.

MERCK & CO., INC.                           AXYS PHARMACEUTICAL, INC.



By: /s/ Mervyn Turner                       By: /s/ Michael Venuti  3/15/00
   --------------------------------            ---------------------------------


[ * ] = CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY
BRACKETS, HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE
COMMISSION PURSUANT TO RULE 24B-2 OF THE SECURITIES EXCHANGE ACT OF 1934, AS
AMENDED.


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