<PAGE>
                                                                  Exhibit 10.67

*CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY
BRACKETS, HAS BEEN OMITTED AND FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 OF THE SECURITIES ACT OF 1933, AS AMENDED.


VIA FACSIMILE AND FEDERAL EXPRESS

August 6, 2001

Mr. Kazuhiro Endo, Product Planning
Zenyaku Kogyo Co., Ltd.
6-16, Otsuka 5-chome
Bunkyo-ku, Tokyo 112-8650
JAPAN



         LETTER AGREEMENT REGARDING DEVELOPMENT AND LICENSE AGREEMENT
         (THE "AGREEMENT"), ENTERED INTO ON AUGUST 16, 1999, BETWEEN ZENYAKU
         KOGYO., LTD. ("ZENYAKU") AND CORIXA CORPORATION ("CORIXA")

Dear Endo-san:

         It was a pleasure to meet with you at our South San Francisco offices
on May 11, 2001. I thought that we had a productive meeting concerning Corixa's
PVAC development program.

         As we discussed during our meeting, based on [*], Corixa [*]. To
further examine the clinical efficacy of PVAC treatment, Corixa is currently
designing an additional US Phase II clinical trial in a selected population of
psoriasis patients.

         We believe that following your review of the data and reports that we
have provided you from the recent Phase II study, you will [*].

--------
*  Confidential Treatment Requested.
<PAGE>
         Because of [*] Zenyaku may defer the payments that were due under
Section 5.1 of the Agreement on November 16, 2000 and February 16, 2001. Those
payments would be due instead as follows:

         (a)      $[*] will be payable within thirty (30) days following
                  Corixa's written notice to Zenyaku of the [*].


         (b)      $[*]will be payable within thirty (30) days following Corixa's
                  delivery to Zenyaku of the [*]. This payment shall be
                  guaranteed and payable even in the event Zenyaku exercises the
                  termination right set forth below.

         Corixa acknowledges that Zenyaku paid to Corixa $[*] under Section 5.1
of the Agreement and the $[*] milestone payable under Section 5.3 of the
Agreement (less $[*] of withholding tax required by the Japanese tax
authorities), which became due as per the two Letter Agreements dated February
16, 2000 and March 30, 2000, between the Parties. Subject to all terms and
conditions of the Agreement, all payments due under Section 5.1 on and after
August 16, 2001 shall be due as set forth therein.

         Further in connection with Corixa's decision to proceed with an
additional U.S. Phase II clinical trial, we agree that Zenyaku shall have an
additional right to terminate the Agreement under Section 18.4 of the Agreement
at any time during the [*] period following Corixa's delivery to Zenyaku of the
final report of the next US Phase II clinical trial, which right to terminate
shall be (i) exercisable by Zenyaku providing Corixa written notice thereof and
(ii) effective [*] following Corixa's receipt of such notice. Any such
termination shall have the same effect as any other termination contemplated by
Sections 5.1 and 18.4(ii); provided, however, that the delayed payments made to
Corixa that were otherwise due on November 16, 2000 and February 16, 2001 shall
not be considered in calculating the amount that Zenyaku has paid to Corixa
under Section 5.1 from August 16, 2001 up until the date of such termination.

         Except as modified hereby, all other terms and conditions of the
Agreement shall remain in full force and effect.

         This Letter Agreement shall be governed by the laws of the state of
Washington, without regard to conflicts of law principles.


--------
*  Confidential Treatment Requested.
<PAGE>
         We hope that you will find the foregoing proposal acceptable. If so,
please confirm your acceptance by signing this Letter Agreement and returning it
to the undersigned.




                                          Sincerely,


                                          CORIXA CORPORATION



                                          By: /s/ Steven Gillis
                                             ----------------------------------
                                          Steven Gillis
                                          Chairman & CEO

ACKNOWLEDGED AND AGREED:

ZENYAKU KOGYO, CO., LTD.

By: /s/ Kazuhiro Hashimoto
   --------------------------------
Its   Kazuhiro Hashimoto
      President & CEO