<PAGE>   1

       As filed with the Securities and Exchange Commission on October ___, 1999
                                                      Registration No. 333-_____
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                ----------------

                                    FORM S-8

                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

                                ----------------

                               CORIXA CORPORATION
             (Exact name of Registrant as specified in its charter)

             DELAWARE                                 91-1654387
     (State of incorporation)            (I.R.S. Employer Identification No.)

                         1124 COLUMBIA STREET, SUITE 200
                                SEATTLE, WA 98104
                    (Address of principal executive offices)

                             -----------------------

              RIBI IMMUNOCHEM RESEARCH, INC. 1986 STOCK OPTION PLAN
            RIBI IMMUNOCHEM RESEARCH, INC. 1996 DIRECTOR OPTION PLAN
              RIBI IMMUNOCHEM RESEARCH, INC. 1996 STOCK OPTION PLAN
                            (Full title of the Plan)

                             -----------------------

                                  STEVEN GILLIS
                      PRESIDENT AND CHIEF EXECUTIVE OFFICER
                               CORIXA CORPORATION
                         1124 COLUMBIA STREET, SUITE 200
                                SEATTLE, WA 98104
                                 (206) 754-5711
 (Name, address and telephone number, including area code, of agent for service)

                             -----------------------
                                    Copy to:

                            William W. Ericson, Esq.
                                Venture Law Group
                           A Professional Corporation
                               4750 Carillon Point
                               Kirkland, WA 98033
                                 (425) 739-8700

               (Calculation of Registration Fee on following page)

<PAGE>   2

CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>
                                                         Proposed        Proposed
                                                          Maximum         Maximum
                                            Maximum      Offering        Aggregate      Amount of
                                          Amount to be   Price Per       Offering      Registration
Title of Securities to be Registered       Registered      Share           Price           Fee
--------------------------------------- --------------- ------------- --------------- -------------
<S>                                     <C>             <C>           <C>             <C>
RIBI IMMUNOCHEM RESEARCH, INC.
    1986 STOCK OPTION PLAN (1)

  Common Stock of Registrant,
  $0.001 par value..................    131,643 Shares   $33.65(2)     $4,430,132(2)   $1,231.58(2)

RIBI IMMUNOCHEM RESEARCH, INC.
    1996 DIRECTOR OPTION PLAN (1)

  Common Stock of Registrant,
  $0.001 par value..................    125,952 Shares   $23.93(2)     $3,013,701(2)   $  837.81(2)

RIBI IMMUNOCHEM RESEARCH, INC.
    1996 STOCK OPTION PLAN (1)

  Common Stock of Registrant,
  $0.001 par value..................     38,927 Shares   $21.88(2)     $  830,258(2)   $  230.81(2)
</TABLE>

-----------------------

(1)  Pursuant to the Agreement and Plan of Merger dated as of June 9, 1999 by
     and among Registrant and Ribi Immunochem Research, Inc., a Delaware
     corporation ("Ribi"), Registrant assumed, effective October 6, 1999, all of
     the outstanding options to purchase Common Stock of Ribi under the Ribi
     Immunochem Research, Inc. 1986 Stock Option Plan, Ribi Immunochem Research,
     Inc. 1996 Director Option Plan and Ribi Immunochem Research, Inc. 1996
     Stock Option Plan, and such options became exercisable to purchase shares
     of Registrant's Common Stock, with appropriate adjustments to the number of
     shares and exercise price of each assumed option.

(2)  Computed in accordance with Rule 457(h) under the Securities Act of 1933,
     as amended (the "Securities Act"), solely for the purpose of calculating
     the registration fee. The computation is based upon the weighted average
     per share exercise price (rounded to the nearest cent) of outstanding
     options under the referenced plan, the shares issuable under which are
     registered hereby.


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<PAGE>   3

                                     PART II
               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3. INCORPORATION OF DOCUMENTS BY REFERENCE.

        The following documents filed with the Securities and Exchange
Commission (the "Commission") are hereby incorporated by reference:

        (a) Registrant's Annual Report on Form 10-K filed with the Commission on
March 22, 1999 for the fiscal year ended December 31, 1998 pursuant to Section
13(a) of the Securities Exchange Act of 1934, as amended (the "Exchange Act"),
which contains audited financial statements for Registrant's latest fiscal year
for which such statements have been filed.

        (b) All other reports filed pursuant to Section 13(a) or 15(d) of the
Exchange Act since the end of the fiscal year covered by the document referred
to in (a) above.

        (c) The description of the Registrant's Common Stock contained in the
Registrant's Registration Statement on Form 8-A filed with the Commission under
Section 12 of the Exchange Act on September 22, 1997, including any amendment or
report filed for the purpose of updating such description.

        All documents filed by Registrant pursuant to Sections 13(a), 13(c), 14
or 15(d) of the Exchange Act after the date hereof, and prior to the filing of a
post-effective amendment which indicates that all securities offered hereunder
have been sold or which deregisters all securities then remaining unsold under
this registration statement, shall be deemed to be incorporated by reference
herein and to be part hereof from the date of filing of such document. Any
statement contained in a document incorporated by reference herein shall be
deemed to be modified or superseded for purposes hereof to the extent that a
statement contained herein (or in any other subsequently file document which
also is incorporated by reference herein) modifies or supersedes such statement.
Any such statement so modified or superseded shall not be deemed to constitute a
part hereof, except as so modified or superseded.

Item 4. DESCRIPTION OF SECURITIES. Not applicable.

Item 5. INTERESTS OF NAMED EXPERTS AND COUNSEL. Not applicable.

Item 6. INDEMNIFICATION OF DIRECTORS AND OFFICERS.

        Section 145 of the Delaware General Corporation Law ("DGCL") authorizes
a court to award or a corporation's Board of Directors to grant indemnification
to directors and officers in terms sufficiently broad to permit such
indemnification under certain circumstances for liabilities (including
reimbursement for expenses incurred) arising under the Securities Act. Article
VI, Sections 6.1 and 6.2 of the Registrant's Bylaws provides for mandatory
indemnification of its directors and officers and permissible indemnification of
employees to the maximum extent permitted by the DGCL. The Registrant's
Certificate of Incorporation provides that, pursuant to Delaware law, its
directors shall not be liable for monetary damages to the Registrant and its
stockholders for breach of the directors' fiduciary duty. This provision in the
Certificate of Incorporation does not eliminate the directors' fiduciary duty,
and in appropriate circumstances equitable remedies such as injunctive or other
forms of non-monetary relief will remain available under Delaware law. In
addition, each director will continue to be subject to a liability for breach of
the director's duty of loyalty to the Registrant for acts or omissions not in
good faith or involving intentional misconduct, for knowing violations of law,
for actions leading to improper personal benefit to the director, and for
payment of dividends or approval of stock repurchases or redemptions that are
unlawful under Delaware law. The provision also does not affect a director's
responsibilities under any other law, such as the federal securities laws or
state or federal environmental laws. The Registrant has entered into
Indemnification Agreements with its officers and directors which provide such
officers and directors with further indemnification to the maximum extent
permitted by the DGCL.


                                      -3-
<PAGE>   4

Item 7. EXEMPTION FROM REGISTRATION CLAIMED. Not applicable.

Item 8. EXHIBITS.

<TABLE>
<CAPTION>
Exhibit
Number
-------
<S>          <C>
  5.1        Opinion of Venture Law Group, A Professional Corporation.

 23.1        Consent of Venture Law Group, A Professional Corporation
             (included in Exhibit 5.1).

 23.2        Consent of Ernst & Young LLP, Independent Auditors.

 23.3        Consent of Ernst & Young LLP, Independent Auditors.

 23.4        Consent of Ernst & Young LLP, Independent Auditors.

 23.5        Consent of KPMG LLP, Independent Auditors.

 24.1        Powers of Attorney (see page 6).
</TABLE>


                                      -4-
<PAGE>   5

Item 10 UNDERTAKINGS.

        The undersigned Registrant hereby undertakes:

                (1) To file, during any period in which offers or sales are
being made, a post-effective amendment to this registration statement to include
any material information with respect to the plan of distribution not previously
disclosed in the registration statement or any material change to such
information in the registration statement.

                (2) That, for purposes of determining any liability under the
Securities Act, each such post-effective amendment shall be deemed to be a new
registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

                (3) To remove from registration by means of a post-effective
amendment any of the securities being registered which remain unsold at the
termination of the offering.

        The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
Registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Exchange Act that is incorporated by reference in the registration statement
shall be deemed to be a new registration statement relating to the securities
offered therein, and the offering of such securities at that time shall be
deemed to be the initial bona fide offering thereof.

        Insofar as the indemnification for liabilities arising under the
Securities Act may be permitted to directors, officers and controlling persons
of the Registrant pursuant to the foregoing provisions, or otherwise, the
Registrant has been advised that in the opinion of the Commission such
indemnification is against public policy as expressed in the Securities Act and
is, therefore, unenforceable. In the event that a claim for indemnification
against such liabilities (other than the payment by the Registrant of expenses
incurred or paid by a director, officer or controlling person of the Registrant
in the successful defense of any action, suit or proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered hereunder, the Registrant will, unless in the opinion of its counsel
the matter has been settled by controlling precedent, submit to a court of
appropriate jurisdiction the question of whether such indemnification by it is
against public policy as expressed in the Securities Act and will be governed by
the final adjudication of such issue.


                                      -5-
<PAGE>   6

                                   SIGNATURES

        Pursuant to the requirements of the Securities Act of 1933, as amended,
Registrant certifies that it has reasonable grounds to believe that it meets all
of the requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Seattle, State of Washington, on this 21st day of
October, 1999.

                                       Corixa Corporation

                                       By: /s/ STEVEN GILLIS
                                          --------------------------------------
                                          Steven Gillis
                                          President and Chief Executive Officer

                                POWER OF ATTORNEY

        KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature
appears below constitutes and appoints Steven Gillis and Michelle Burris,
jointly and severally, his or her attorneys-in-fact and agents, each with the
power of substitution and resubstitution, for him or her and in his or her name,
place or stead, in any and all capacities, to sign any amendments to this
Registration Statement on Form S-8, and to file such amendments, together with
exhibits and other documents in connection therewith, with the Securities and
Exchange Commission, granting to each attorney-in-fact and agent, full power and
authority to do and perform each and every act and thing requisite and necessary
to be done in and about the premises, as fully as he or she might or could do in
person, and ratifying and confirming all that the attorney-in-facts and agents,
or his or her substitute or substitutes, may do or cause to be done by virtue
hereof.

        Pursuant to the requirements of the Securities Act of 1933, as amended,
this Registration Statement has been signed by the following persons in the
capacities and on the dates indicated.

<TABLE>
<CAPTION>
            Signature                             Title                                 Date
            ---------                             -----                                 ----
<S>                                <C>                                            <C>
/s/ Steven Gillis                  President, Chief Executive Officer             October 21, 1999
-----------------------------      and Director (Principal Executive Officer)
Steven Gillis

/s/ Michelle Burris                Vice President and Chief Financial Officer     October 21, 1999
-----------------------------      (Principal Financial and Accounting Officer)
Michelle Burris

/s/ Mark McDade                    Director                                       October 21, 1999
-----------------------------
Mark McDade

/s/ Joseph S. Lacob                Director                                       October 21, 1999
-----------------------------
Joseph S. Lacob

/s/ Arnold L. Oronsky              Director                                       October 21, 1999
-----------------------------
Arnold L. Oronsky

/s/ Andrew E. Senyei               Director                                       October 21, 1999
-----------------------------
Andrew E. Senyei
</TABLE>


                                      -6-
<PAGE>   7

                               INDEX TO EXHIBITS

<TABLE>
<CAPTION>
Exhibit                                                                     Page
Number                                                                      No.
-------                                                                     ----
<S>          <C>                                                            <C>
  5.1        Opinion of Venture Law Group, A Professional Corporation.

 23.1        Consent of Venture Law Group, A Professional Corporation
             (included in Exhibit 5.1).

 23.2        Consent of Ernst & Young LLP, Independent Auditors.

 23.3        Consent of Ernst & Young LLP, Independent Auditors.

 23.4        Consent of Ernst & Young LLP, Independent Auditors.

 23.5        Consent of KPMG LLP, Independent Auditors.

 24.1        Powers of Attorney (see page 6).
</TABLE>


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