<PAGE>
                                                                    Exhibit 10.3

* 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.

                            STOCK PURCHASE AGREEMENT

                               CORIXA CORPORATION

                                OCTOBER 26, 2001


<PAGE>

                                TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                            PAGE
                                                                            ----
<S>      <C>                                                                <C>
1.       PURCHASE AND SALE.....................................................1

         1.1      Sale of Shares...............................................1

         1.2      Options of Corixa............................................2

         1.3      Closing Dates................................................2

         1.4      Delivery.....................................................3

         1.5      Rule 144 Reporting...........................................3

         1.6      "Market Stand-Off" Agreements................................3

         1.7      Standstill Covenant..........................................3

         1.8      Cooperation To Satisfy Closing Conditions....................4

2.       REPRESENTATIONS AND WARRANTIES OF CORIXA..............................4

         2.1      Organization and Standing; Certificate and Bylaws............4

         2.2      Authorization................................................4

         2.3      Validity of Shares...........................................4

         2.4      Offering.....................................................4

         2.5      SEC Documents................................................4

         2.6      No Conflict; No Violation....................................5

         2.7      Consents and Approvals.......................................5

         2.8      Absence of Certain Developments..............................5

3.       REPRESENTATIONS AND WARRANTIES OF PURCHASER...........................6

         3.1      Authorization................................................6

         3.2      Investment Representations...................................6

4.       CONDITIONS TO CLOSING.................................................7

         4.1      Conditions to Obligations of Purchaser.......................7

         4.2      Conditions to Obligations of Corixa..........................8

5.       MISCELLANEOUS.........................................................8

         5.1      Dispute Resolution...........................................8

         5.2      Limitation of Liability......................................9

         5.3      Governing Law................................................9

         5.4      Successors and Assigns.......................................9

         5.5      Entire Agreement.............................................9
</TABLE>

                                      -i-

<PAGE>

                                TABLE OF CONTENTS
                                   (continued)

<TABLE>
<CAPTION>
                                                                            PAGE
                                                                            ----
<S>      <C>                                                                <C>
         5.6      Severability.................................................9

         5.7      Amendment and Waiver.........................................9

         5.8      Delays or Omissions..........................................9

         5.9      Notices, etc................................................10

         5.10     Finder's Fees...............................................10

         5.11     Information Confidential....................................11

         5.12     Titles and Subtitles........................................11

         5.13     Counterparts................................................11
</TABLE>

                                      -ii-

<PAGE>


                            STOCK PURCHASE AGREEMENT

        THIS STOCK PURCHASE AGREEMENT (the "AGREEMENT") is made and entered into
as of October 26, 2001, by and between CORIXA CORPORATION, a Delaware
corporation ("CORIXA"), and AMERSHAM HEALTH, INC., a Delaware corporation
("PURCHASER").

                                    RECITALS

        A. Corixa and Amersham PLC (an affiliate of Purchaser) are parties to
that certain Development, Commercialization and License Agreement of even date
herewith (the "LICENSE AGREEMENT").

        B. Corixa and Amersham PLC are parties to that certain Manufacturing and
Supply Agreement of even date herewith (the "MANUFACTURING AGREEMENT").

        C. Pursuant to Section 8.1 of the License Agreement, Purchaser has
agreed to purchase an aggregate of $15,000,000 of common stock, $0.001 par value
per share, of Corixa (the "COMMON STOCK") in accordance with the terms and
conditions of this Agreement.

        NOW, THEREFORE, the Parties hereto agree as follows:

        1. PURCHASE AND SALE.

        Subject to the terms and conditions hereof, and in reliance upon the
representations, warranties and agreements contained herein, Corixa hereby
agrees to issue and sell to Purchaser, and Purchaser hereby agrees to purchase
from Corixa, the aggregate number of shares of Common Stock determined in
accordance with Section 1.1 hereof.

            1.1 SALE OF SHARES. On the First Closing Date (as defined in Section
1.3), Corixa shall issue and sell to Purchaser, and Purchaser shall purchase
from Corixa that number of shares of Common Stock (the "First Closing Shares")
equal to the quotient of [*] divided by the First Closing Purchase Price (as
hereinafter defined). At the sole option of Corixa and subject to Section 1.2,
on the Second Closing Date (as defined in Section 1.3), Corixa shall issue and
sell to Purchaser, and Purchaser shall purchase from Corixa that number of
shares of Common Stock (the "Second Closing Shares") equal to the quotient of
[*] divided by the Second Closing Purchase Price (as hereinafter defined). At
the sole option of Corixa and subject to Section 1.2, on the Third Closing Date
(as defined in Section 1.3), Corixa shall issue and sell to Purchaser, and
Purchaser shall purchase from Corixa that number of shares of Common Stock (the
"Third Closing Shares") equal to the quotient of [*] divided by the Third
Closing Purchase Price (as hereinafter defined). In the event the number of
First Closing Shares, Second Closing Shares or Third Closing Shares includes a
fraction of a share, the number of First Closing Shares, Second Closing Shares
or Third Closing Shares (as applicable) shall be increased to the nearest whole
number of shares and the aggregate First Closing Purchase Price, Second Closing
Purchase Price or Third Closing Purchase Price (as applicable) shall be
increased to equal the First Closing Purchase Price, Second Closing Purchase
Price or Third Closing Purchase Price (as


--------
* Confidential Treatment Requested.


<PAGE>


applicable) times such whole number of shares. The "First Closing Purchase
Price" shall equal [*] percent ([*]%) of the average of the closing prices of
the Common Stock on the Nasdaq National Market, as reported by the Wall Street
Journal, Western Edition (the "Wall Street Journal"), for the [*] trading days
prior to the date of this Agreement and the [*] trading days following and
including the date of this Agreement. The "Second Closing Purchase Price" and
"Third Closing Purchase Price" (as applicable) shall equal the average of the
closing prices of the Common Stock on the Nasdaq National Market, as reported by
the Wall Street Journal for the [*] trading days prior to the Notice Date (as
defined in Section 1.2) and the [*] trading days following and including the
Notice Date.

            1.2 OPTIONS OF CORIXA.

                (a) Purchaser hereby grants Corixa the irrevocable options to
cause Purchaser to purchase (i) the Second Closing Shares at a price per share
equal to the Second Closing Purchase Price and (ii) the Third Closing Shares at
a price per share equal to the Third Closing Purchase Price (together, the
"Options"). Corixa may exercise the Options at any time during a period of 18
months following the date of this Agreement; provided however, that Corixa shall
not exercise the Options within [*] of each other nor shall Corixa exercise more
than one (1) Option in the year 2001. In the event of termination of the License
Agreement and the Manufacturing Agreement, the Options will remain in full
effect and be legally binding obligations of Purchaser.

                (b) To exercise the Options with respect to the Second Closing
Shares or the Third Closing Shares, Corixa shall notify Purchaser in writing (an
"Exercise Notice") specifying the exercise of such Option. The date of delivery
of such Exercise Notice to Purchaser is referred to as the applicable "Notice
Date," and the Option shall be deemed to have been validly exercised on such
Notice Date with respect to the Second Closing Shares or the Third Closing
Shares.

            1.3 CLOSING DATES. The closing of the sale and purchase of the First
Closing Shares (the "First Closing") shall take place on the [*] business day
after the date of this Agreement or such later date as Corixa and Purchaser may
mutually agree or as may be specified in accordance with the last sentence of
this section (the "First Closing Date"). The closing of the sale and purchase of
the Second Closing Shares and the Third Closing Shares (the "Second Closing" and
"Third Closing," respectively) shall take place on the [*] business day after
the applicable Notice Date or such later date as Corixa and Purchaser may
mutually agree or as may be specified in accordance with the last sentence of
this section (the "Second Closing Date" and "Third Closing Date," respectively).
As used hereinafter, the terms "Closing" and "Closing Date" shall refer to the
First, Second or Third Closing and the First, Second or Third Closing Date, as
the context requires; the term "Shares" shall refer to the First, Second and
Third Closing Shares collectively or the First, Second or Third Closing Shares,
if and as the context requires; and the term "Purchase Price" shall refer to the
First, Second and Third Closing Purchase Price collectively or the First, Second
or Third Closing Purchase Price, if and as the context requires. If for any
reason Corixa is unable to satisfy the closing conditions set forth in Section 4
of this


--------
* Confidential Treatment Requested.

                                      -2-


<PAGE>

Agreement as of the scheduled Closing Date, then Corixa shall use its best
efforts to satisfy such conditions at the earliest practicable date, and the
Closing Date shall be rescheduled to such date as Corixa may specify (with at
least five (5) business days prior notice to Purchaser) on which Corixa can
satisfy such closing conditions.

            1.4 DELIVERY. At the Closing, Corixa will execute and deliver to
Purchaser a certificate registered in the name of Purchaser, representing the
Shares to be purchased by Purchaser from Corixa, dated the Closing Date, against
payment of the aggregate Purchase Price for the Shares, by wire transfer, a
check made payable to the order of Corixa, or any combination thereof.

            1.5 RULE 144 REPORTING. With a view to making available to Purchaser
the benefits of certain rules and regulations of the Securities and Exchange
Commission (the "SEC") which may permit the sale of the Shares to the public
without registration, Corixa agrees to use its best efforts to:

                (a) Make and keep public information available, as those terms
are understood and defined in Rule 144 ("Rule 144") under the Securities Act of
1933, as amended (the 1933 Act") or any similar or analogous rule promulgated
under the 1933 Act, as long as the Shares are outstanding;

                (b) File with the SEC, in a timely manner, all reports and other
documents required of Corixa under the 1933 Act and the Securities Exchange Act
of 1934, as amended (the "1934 Act");

                (c) Take all such action (including without limitation the
furnishing of the information described in Rule 144(d)(4)) as may be necessary
to facilitate a sale of the shares by Purchaser to a "qualified institutional
buyer," as such term is defined in Rule 144A of the 1933 Act.

            1.6 "MARKET STAND-OFF" AGREEMENTS. Purchaser hereby agrees that
prior to the second anniversary of the First Closing Date, Second Closing Date
or Third Closing Date, as applicable, it shall not sell or otherwise transfer or
dispose of any of the First Closing Shares, Second Closing Shares or Third
Closing Shares, as applicable held by it. Corixa may impose stop-transfer
instructions with respect to securities subject to the foregoing restriction
until the expiration thereof. Following [*] of the First Closing Date, until
[*], if Purchaser desires to sell or otherwise transfer any Shares, then
Purchaser shall first give 5 days' written notice thereof to Corixa, describing
generally the basis upon which Purchaser proposes to sell or otherwise transfer
or dispose of such Shares.

            1.7 STANDSTILL COVENANT. Other than the purchase of the Shares
contemplated by Section 1 of this Agreement, Purchaser agrees that, during the
term of the License Agreement and Manufacturing Agreement and for [*]
thereafter, neither Purchaser nor any of its affiliates will in any manner,
directly or indirectly, without the written consent of the Company effect,
propose to effect or actively and consciously participate as a partner in (a)
any acquisition of any securities or assets of Corixa or (b) any tender or
exchange offer, merger, business combination, recapitalization or other
extraordinary transaction involving Corixa unless an unaffiliated third



* Confidential Treatment Requested.
                                      -3-
<PAGE>

party has already made an offer for all of the outstanding shares of Corixa and
neither Purchaser nor any of its affiliates possess any prior knowledge of, or
is involved in any manner with such an offer.

            1.8 COOPERATION TO SATISFY CLOSING CONDITIONS. If any actions are
required to satisfy the closing conditions set forth herein, the Parties shall
take such actions as are reasonably required to satisfy such conditions on a
prompt basis.

        2. REPRESENTATIONS AND WARRANTIES OF CORIXA.

        Corixa hereby represents and warrants to Purchaser that the following
matters shall be true as of the Closing:

            2.1 ORGANIZATION AND STANDING; CERTIFICATE AND BYLAWS. Corixa is a
corporation duly organized, validly existing and in good standing under the laws
of the State of Delaware, and has full power and authority to own and operate
its properties and assets and to carry on its business as presently conducted
and as proposed to be conducted. Corixa is qualified as a foreign corporation to
do business in each jurisdiction in the United States in which the ownership of
its property or the conduct of its business requires such qualification, except
where any statutory fines or penalties or any corporate disability imposed for
the failure to qualify would not materially adversely affect Corixa, its assets,
financial condition or operations.

            2.2 AUTHORIZATION. All corporate action on the part of Corixa, its
officers, directors and stockholders necessary for the authorization, execution
and delivery of this Agreement, the performance of all Corixa's obligations
hereunder, and for the authorization, issuance, sale and delivery of the Shares
has been taken or will be taken prior to Closing. This Agreement, when executed
and delivered, shall constitute a valid and legally binding obligation of Corixa
in accordance with its terms, subject to laws of general application relating to
bankruptcy, insolvency and the relief of debtors, and subject to general equity
principles.

            2.3 VALIDITY OF SHARES. The Shares being purchased by Purchaser
hereunder will, upon issuance pursuant to the terms hereof, be duly authorized
and validly issued, fully paid and nonassessable; provided, however, that the
Shares may be subject to restrictions on transfer under state and/or federal
securities laws as set forth herein or as otherwise required by such laws at the
time a transfer is proposed.

            2.4 OFFERING. Assuming the accuracy of the representations and
warranties of Purchaser contained in Section 3 hereof, the offer, issue, and
sale of Shares are exempt from the registration and prospectus delivery
requirements of the 1933 Act, and the Shares are exempt from registration and
qualification under the registration, permit, or qualification requirements of
all applicable state securities laws.

            2.5 SEC DOCUMENTS.

                (a) As of the First Closing, Corixa will have furnished to
Purchaser the following documents, and the information contained in such
documents, as of their respective dates (or if amended, as of the date of such
amendment), will not contain any untrue statement of

                                      -4-
<PAGE>

a material fact, and will not omit to state any material fact necessary to make
any statement, in light of the circumstances under which such statement was
made, not misleading:

        Corixa's most recent annual report on Form 10-K, together with its proxy
statement for its 2001 Annual Meeting of Stockholders and any additional
Quarterly Reports on Form 10-Q or Current Reports on Form 8-K filed after the
date of such annual report on Form 10-K but prior to the First Closing.

                (b) As of the Second Closing Date, Corixa shall have furnished
to Purchaser the following documents, and the information contained in such
documents, as of their respective dates (or, if amended, as of the date of
amendment), will not contain any untrue statement of a material fact, or omit to
state a material fact necessary to make any statement, in light of the
circumstances under which such statement is made, not misleading.

        Corixa's most recent annual report on Form 10-K, together with its most
recent proxy statement for its Annual Meeting of Stockholders and any additional
Quarterly Reports on form 10-Q or Current Reports on Form 8-K filed after the
date of such annual report on Form 10-K but prior to the Second Closing.

                (c) As of the Third Closing Date, Corixa shall have furnished to
Purchaser the following documents, and the information contained in such
documents, as of their respective dates (or, if amended, as of the date of
amendment), will not contain any untrue statement of a material fact, or omit to
state a material fact necessary to make any statement, in light of the
circumstances under which such statement is made, not misleading.

        Corixa's most recent annual report on Form 10-K, together with its most
recent proxy statement for its Annual Meeting of Stockholders and any additional
Quarterly Reports on form 10-Q or Current Reports on Form 8-K filed after the
date of such annual report on Form 10-K but prior to the Third Closing.

            2.6 NO CONFLICT; NO VIOLATION. The execution, delivery and
performance of this Agreement and consummation of the transactions contemplated
hereby will not (a) conflict with any provisions of the Certificate of
Incorporation or Bylaws of Corixa; (b) result in any material violation or
default of, or permit the acceleration of any obligation under (in each case,
upon the giving of notice, the passage of time, or both), any material mortgage,
indenture, lease, agreement or other instrument, permit, franchise, license,
judgment, order, decree, law, ordinance, rule or regulation applicable to Corixa
or its properties.

            2.7 CONSENTS AND APPROVALS. All consents, approvals, orders, or
authorizations of, or registrations, qualifications, designations, declarations,
or filings with, any governmental authority, required on the part of Corixa in
connection with the valid execution and delivery of this Agreement, the offer,
sale or issuance of the Shares, or the consummation of any other transaction
contemplated hereby have been obtained, or will be effective at the Closing,
except for notices required or permitted to be filed with certain state and
federal securities commissions after the Closing, which notices will be filed on
a timely basis.

            2.8 ABSENCE OF CERTAIN DEVELOPMENTS. As of the Closing, since the
date of the balance sheet set forth in Corixa's most recent annual report on
Form 10-K or Quarterly

                                      -5-
<PAGE>

Report on Form 10-Q referred to Section 2.5, except as Corixa may specify in a
Schedule of Exceptions provided to Purchaser promptly before the Closing, Corixa
shall not have (a) incurred or become subject to any material liabilities
(absolute or contingent) except current liabilities incurred, and liabilities
under contracts entered into, in the ordinary course of business, consistent
with past practices; (b) mortgaged, pledged or subjected to lien, charge or any
other encumbrance any of its assets, tangible or intangible; (c) sold, assigned
or transferred any of its material assets or canceled any material debts or
obligations except in the ordinary course of business, consistent with past
practices; (d) suffered any extraordinary losses, or waived any rights of
substantial value; (e) entered into any material transaction other than in the
ordinary course of business, consistent with past practices; or (f) otherwise
had any material change in its condition, financial or otherwise, except for
changes in the ordinary course of business, consistent with past practices, none
of which individually or in the aggregate has been materially adverse to Corixa.

        3. REPRESENTATIONS AND WARRANTIES OF PURCHASER.

        Purchaser hereby represents and warrants to Corixa as follows:

            3.1 AUTHORIZATION. All corporate action on the part of Purchaser,
its officers, directors and stockholders necessary for the authorization,
execution and delivery of this Agreement and the performance of all Purchaser's
obligations hereunder has been taken or will be taken prior to Closing. This
Agreement, when executed and delivered, shall constitute a valid and legally
binding obligation of Purchaser in accordance with its terms, subject to laws of
general application relating to bankruptcy, insolvency and the relief of
debtors, and subject to general equity principles.

            3.2 INVESTMENT REPRESENTATIONS.

                (a) Purchaser is acquiring the Shares for its own account, not
as nominee or agent, for investment and not with a view to, or for resale in
connection with, any distribution or public offering thereof within the meaning
of the 1933 Act.

                (b) Purchaser understands that (i) the Shares have not been
registered under the 1933 Act by reason of a specific exemption therefrom, that
the Shares must continue to be held by Purchaser, and that Purchaser must,
therefore, bear the economic risk of such investment indefinitely, unless a
subsequent disposition thereof is registered under the 1933 Act or is exempt
from such registration; (ii) the exemptions from registration afforded by Rule
144 (the provisions of which are known to it) promulgated under the 1933 Act
depend on the satisfaction of various conditions, and that, if applicable, Rule
144 may afford the basis for sales only in limited amounts; (iii) each
certificate representing the Shares will be endorsed with the following legend:

                "THE SECURITIES EVIDENCED BY THIS CERTIFICATE HAVE NOT BEEN
        REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND MAY NOT BE
        SOLD, TRANSFERRED, ASSIGNED OR HYPOTHECATED UNLESS (A) PURSUANT TO SEC
        RULE 144 OR (B) THERE IS AN EFFECTIVE REGISTRATION STATEMENT UNDER SAID
        ACT COVERING SUCH

                                      -6-
<PAGE>

        SECURITIES OR (C) CORIXA RECEIVES AN OPINION OF COUNSEL FOR THE HOLDER
        OF THESE SECURITIES REASONABLY SATISFACTORY TO CORIXA, STATING THAT SUCH
        SALE, TRANSFER, ASSIGNMENT OR HYPOTHECATION IS EXEMPT FROM THE
        REGISTRATION AND PROSPECTUS DELIVERY REQUIREMENTS OF SAID ACT."

And (iv) Corixa will instruct any transfer agent not to register the transfer of
any of the Shares unless the conditions specified in the foregoing legend are
satisfied.

                (c) It has been furnished with such materials and has been given
access to such information relating to Corixa as it or its qualified
representative has requested and it has been afforded the opportunity to ask
questions of and receive answers from the management of Corixa regarding Corixa
and the Shares, all as it has found necessary to make an informed investment
decision.

                (d) Purchaser is an "accredited investor" within the meaning of
Rule 501 of Regulation D promulgated under the 1933 Act and was not organized
for the specific purpose of acquiring the Shares.

                (e) For purposes of the application of state securities laws,
Purchaser represents that it is a corporation organized and existing under the
laws of the state of Delaware.

        4. CONDITIONS TO CLOSING.

            4.1 CONDITIONS TO OBLIGATIONS OF PURCHASER. Purchaser's obligation
to purchase the First Closing Shares at the First Closing, the Second Closing
Shares at the Second Closing and the Third Closing Shares at the Third Closing
is in each case subject to the fulfillment, at or prior to the applicable
Closing, of the following conditions:

                (a) REPRESENTATIONS AND WARRANTIES TRUE. The representations and
warranties made by Corixa in Section 2 hereof shall be true and correct in all
material respects on the date of the Closing with the same force and effect as
if they had been made on and as of said date.

                (b) PERFORMANCE OF OBLIGATIONS. Corixa shall have performed all
obligations and conditions herein required to be performed by it on or prior to
the Closing.

                (c) PROCEEDINGS AND DOCUMENTS. All corporate and other
proceedings in connection with the transactions contemplated at the Closing
hereby and all documents and instruments incident to such transactions shall be
reasonably satisfactory in substance and form to Purchaser and its counsel, and
Purchaser and its counsel shall have received all such counterpart originals or
certified or other copies of such documents as they may reasonably request.

                (d) QUALIFICATIONS, LEGAL INVESTMENT. All authorizations,
approvals, or permits, if any, of any governmental authority or regulatory body
of the United States or of any state that are required in connection with the
lawful sale and issuance of the Shares pursuant to this Agreement shall have
been duly obtained and shall be effective on and as of the Closing.


                                      -7-
<PAGE>

No stop order or other order enjoining the sale of the Shares shall have been
issued and no proceedings for such purpose shall be pending or, to the knowledge
of Corixa, threatened by the SEC or any commissioner of corporations or similar
officer of any other state having jurisdiction over this transaction. At the
time of the Closing, the sale and issuance of the Shares shall be legally
permitted by all laws and regulations to which Purchaser and Corixa are subject.

                (e) COMPLIANCE CERTIFICATE. Corixa shall have delivered to
Purchaser a Certificate, executed by an officer of Corixa, dated the date of the
Closing, certifying to the fulfillment of the conditions specified in
subparagraphs (a) and (b) of this Subsection 4.1.

            4.2 CONDITIONS TO OBLIGATIONS OF CORIXA. Corixa's obligation to
issue and sell the First Closing Shares at the First Closing, the Second Closing
Shares at the Second Closing and the Third Closing Shares at the Third Closing
is in each case subject to the fulfillment to Corixa's satisfaction, at or prior
to the applicable Closing, of the following conditions:

                (a) REPRESENTATIONS AND WARRANTIES TRUE. The representations and
warranties made by Purchaser in Section 3 hereof shall be true and correct in
all material respects on the date of the Closing, with the same force and effect
as if they had been made on and as of said date.

                (b) PERFORMANCE OF OBLIGATIONS. Purchaser shall have performed
and complied with all agreements and conditions herein required to be performed
or complied with by it on or before the Closing.

                (c) QUALIFICATIONS, LEGAL INVESTMENT. All authorizations,
approvals, or permits, if any, of any governmental authority or regulatory body
of the United States or of any state that are required in connection with the
lawful sale and issuance of securities pursuant to this Agreement shall have
been duly obtained and shall be effective on and as of the Closing. No stop
order or other order enjoining the sale of the Shares shall have been issued and
no proceedings for such purpose shall be pending or, to the knowledge of Corixa,
threatened by the SEC or any commissioner of corporations or similar officer of
any other state having jurisdiction over this transaction. At the time of the
Closing, the sale and issuance of the securities hereunder shall be legally
permitted by all laws and regulations to which Purchaser and Corixa are subject.

                (d) COMPLIANCE CERTIFICATE. Purchaser shall have delivered to
Corixa a Certificate, executed by an officer of Purchaser, dated the date of the
Closing, certifying to the fulfillment of the conditions specified in
subparagraphs (a) and (b) of this Subsection 4.2.

        5. MISCELLANEOUS.

            5.1 DISPUTE RESOLUTION. In the event of any controversy or claim
arising out of, relating to or in connection with any provision of this
Agreement, the Parties shall try to settle their differences amicably between
themselves first, by referring the disputed matter to the respective Chief
Financial Officers of each Party and, if not resolved by the Chief Financial
Officers, by referring the disputed matter to the respective Chief Executive
Officers of each Party. Either Party may initiate such informal dispute
resolution by sending written notice of the dispute to the other Party, and,
within 20 days after such notice, such representatives of the

                                      -8-
<PAGE>

Parties shall meet for attempted resolution by good faith negotiations. If such
personnel are unable to resolve a dispute within 30 days of their first meeting
of such negotiations, either Party may seek to have such dispute resolved by
binding arbitration with a single arbitrator under the commercial rules of the
American Arbitration Association. The Parties hereby consent to conduct such
binding arbitration procedures in English in the city of New York, New York.

            5.2 LIMITATION OF LIABILITY. IN NO EVENT SHALL EITHER PARTY, ITS
DIRECTORS, OFFICERS, EMPLOYEES, AGENTS OR AFFILIATES BE LIABLE TO THE OTHER
PARTY FOR ANY INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES,
WHETHER BASED UPON A CLAIM OR ACTION OF CONTRACT, WARRANTY, NEGLIGENCE, STRICT
LIABILITY OR OTHER TORT, OR OTHERWISE, ARISING OUT OF THIS AGREEMENT. For
clarification, the foregoing sentence shall not be interpreted to limit or to
expand the express rights specifically granted in the sections of this
Agreement.

            5.3 GOVERNING LAW. This Agreement shall be governed by and construed
under the laws of the State of Delaware as applied to agreements among Delaware
residents, made and to be performed entirely within the State of Delaware.

            5.4 SUCCESSORS AND ASSIGNS. Except as otherwise expressly provided
herein, the provisions hereof shall inure to the benefit of, and be binding
upon, the successors, assigns, heirs, executors, and administrators of the
parties hereto.

            5.5 ENTIRE AGREEMENT. This Agreement, the License Agreement, the
Manufacturing Agreement and the exhibits hereto and thereto, the Confidentiality
Agreement effective August 10, 2000 between Medi-Physics, Inc. doing business as
Nycomed Amersham Imaging, and the other documents delivered pursuant hereto and
thereto constitute the full and entire understanding and agreement among the
parties with regard to the subjects hereof, and no party shall be liable or
bound to any other party in any manner by any representations, warranties,
covenants, or agreements except as specifically set forth herein or therein.
Nothing in this Agreement, express or implied, is intended to confer upon any
party, other than the parties hereto and their respective successors and
assigns, any rights, remedies, obligations, or liabilities under or by reason of
this Agreement, except as expressly provided herein.

            5.6 SEVERABILITY. In case any provision of this Agreement shall be
invalid, illegal, or unenforceable, it shall, to the extent practicable, be
modified so as to make it valid, legal and enforceable and to retain as nearly
as practicable the intent of the parties, and the validity, legality, and
enforceability of the remaining provisions shall not in any way be affected or
impaired thereby.

            5.7 AMENDMENT AND WAIVER. Any term of this Agreement may be amended
and the observance of any term of this Agreement may be waived (either generally
or in a particular instance, either retroactively or prospectively, and either
for a specified period of time or indefinitely), with the written consent of
Corixa and Purchaser. Any amendment or waiver effected in accordance with this
Section shall be binding upon Purchaser, each future holder of the Shares, and
Corixa.


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<PAGE>

            5.8 DELAYS OR OMISSIONS. No delay or omission to exercise any right,
power, or remedy accruing to Purchaser or any subsequent holder of any Shares
upon any breach, default or noncompliance of Corixa under this Agreement, shall
impair any such right, power, or remedy, nor shall it be construed to be a
waiver of any such breach, default or noncompliance, or any acquiescence
therein, or of any similar breach, default or noncompliance thereafter
occurring. It is further agreed that any waiver, permit, consent, or approval of
any kind or character on Purchaser's part of any breach, default or
noncompliance under this Agreement or any waiver on Purchaser's part of any
provisions or conditions of this Agreement must be in writing and shall be
effective only to the extent specifically set forth in such writing, and that
all remedies, either under this Agreement, by law, or otherwise afforded to
Purchaser, shall be cumulative and not alternative.

            5.9 NOTICES, ETC. All notices and other communications required or
permitted hereunder shall be in writing and shall be deemed effectively given
(a) upon personal delivery, (b) on report of successful transmission by
facsimile machine that automatically generates a printed report indicating
whether transmission was completed successfully, at the conclusion of each
transmission, (c) on the first business day after receipted delivery to a
courier service which guarantees next business-day delivery, under circumstances
in which such guaranty is applicable, or (d) on the earlier of delivery or five
(5) business days after mailing by United States certified mail, postage and
fees prepaid, to the appropriate party at the address set forth below or to such
other address as the part so notifies the other in writing:

            if to Corixa, to:         Corixa Corporation
                                      1124 Columbia Street
                                      Suite 200
                                      Seattle, WA  98104
                                      Attn: Chief Financial Officer
                                      Copy to: General Counsel

            if to Purchaser, to:      Amersham Health, Inc.
                                      101 Carnegie Center
                                      Princeton, NJ 08540
                                      Attn:  General Counsel

            with a copy to:           Amersham PLC
                                      Amersham Place
                                      Little Chalfont
                                      Buckinghamshire
                                      ENGLAND HP7 9NA
                                      Attn:  Group Secretary

        Notwithstanding the foregoing, all notices and other communications to
an address outside of the United States shall be sent by telecopy and confirmed
in writing to be sent by first class mail.

            5.10 FINDER'S FEES.


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<PAGE>

                (a) Corixa (i) represents and warrants that it has retained no
finder or broker in connection with the transactions contemplated by this
Agreement and (ii) hereby agrees to indemnify and to hold Purchaser harmless of
and from any liability for any commission or compensation in the nature of a
finder's fee to any broker or other person or firm (and the costs and expenses
of defending against such liability or asserted liability) for which Corixa or
any of its employees or representatives is responsible.

                (b) Purchaser (i) represents and warrants that it has retained
no finder or broker in connection with the transactions contemplated by this
Agreement, and (ii) hereby agrees to indemnify and to hold Corixa harmless of
and from any liability for any commission or compensation in the nature of a
finder's fee to any broker or other person or firm (and the costs and expenses
of defending against such liability or asserted liability) for which Purchaser
or any of its employees or representatives are responsible.

            5.11 INFORMATION CONFIDENTIAL. Purchaser acknowledges that any non
public information received by it pursuant hereto is confidential and for
Purchaser's use only, and it will refrain from using such information or
reproducing, disclosing, or disseminating such information to any other person
(other than its employees, affiliates, agents, or partners having a need to know
the contents of such information and its attorneys, in each case who agree to be
bound by this Section 5.9), except in connection with the exercise of rights
under this Agreement, unless such information becomes available to the public
generally or it is required by a governmental body to disclose such information.

            5.12 TITLES AND SUBTITLES. The titles of the sections and
subsections of this Agreement are for convenience of reference only and are not
to be considered in construing this Agreement.

            5.13 COUNTERPARTS. This Agreement may be executed in any number of
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one instrument.

        The foregoing Agreement is hereby executed as of the date first above
written.

CORIXA CORPORATION                       AMERSHAM HEALTH, INC.

By:/s/ Steven Gillis                     By:/s/ Jeffrey Freedman
   ---------------------------------         -----------------------------------
Printed Name: Steven Gillis              Printed Name: Jeffrey Freedman
             -----------------------                   ------------------------
Title: Chief Executive Officer           Title: Vice President
      ------------------------------            --------------------------------


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