<PAGE>
                                                           Exhibit 10.22
                                              REDACTED
                                              CONFIDENTIAL TREATMENT REQUESTED


                            ASSET PURCHASE AGREEMENT


     This ASSET PURCHASE AGREEMENT is made and entered into as of January 15,
1997 (the "Agreement") by and between Immunex Corporation, a Washington
corporation ("Immunex"), and SuperGen, Inc., a California corporation
("SuperGen").


                              W I T N E S S E T H:

     WHEREAS, Immunex desires to sell to SuperGen and SuperGen desires to
purchase from Immunex the Purchased Assets (hereinafter defined) upon the terms
and conditions and for the Purchase Price (hereinafter defined) as set forth in
this Agreement;

     NOW, THEREFORE, in consideration of the foregoing premises and the mutual
covenants herein contained, SuperGen and Immunex hereby agree as follows:


ARTICLE 1:  DEFINITIONS

     As used in this Agreement the following defined terms shall have the
meanings set forth below:

     1.1  "Affiliate" means any corporation or business entity of which a party
owns directly or indirectly, fifty percent (50%) or more of the assets or
outstanding stock, or any corporation which a party directly or indirectly
controls, or any parent corporation that owns, directly or indirectly, fifty
percent (50%) or more of the assets or outstanding stock of a party or directly
or indirectly controls a party.

     1.2  "ANDA" means the Abbreviated New Drug Application No. 74-513, filed
with the United States Food and Drug Administration for Etoposide injection,
which is owned/sponsored by Immunex, including all information therein.

     1.3  "Applicable Laws" means all laws, treaties, statutes, ordinances,
judgments, decrees, directives, rules, injunctions, writs, regulations, binding
arbitration rulings, orders, judicial or administrative interpretations or
authorization of, any Governmental Authority having jurisdiction over the
Purchased Assets in the Territory, as may be in effect on the Closing Date.

     1.4  "Closing" shall have the meaning set forth in Section 2.4.

     1.5  "Closing Date" means January 15, 1997 or such other date as is
determined in accordance with Section 2.4.


<PAGE>

     1.6  "Encumbrances" mean all claims, security interests, liens, pledges,
charges, escrows, options, proxies, rights of first refusal, preemptive rights,
mortgages, hypothecations, prior assignments, title retention agreements,
indentures, security agreements or any other encumbrances of any kind.

     1.7  "Etoposide" means the pharmaceutical compound 4'-
demethylepipodophyllotoxin 9-[4,6-0-(R)-ethylidene-B-D-glucopyranoside].

     1.8  "FDA" means the United States Food and Drug Administration.

     1.9  "Governmental Authority" means any governmental department,
commission, board, bureau, agency, court or other instrumentality of the
United States including but not limited to federal, state, district or
commonwealth thereof, any foreign government or any jurisdiction,
municipality or other political subdivision thereof.

     1.10 "Inventory" means Immunex's Etoposide inventory of Product set
forth on Exhibit A.

     1.11 "Know-How" means all data, information, know-how (including without
limitation, processes and methods) relating to the manufacture, testing,
storage, or regulatory status of the Product.

     1.12 "Losses" means any and all damages, fines, liabilities, fees,
penalties, deficiencies, losses and expenses (including, without limitation
interest, court costs, fees of attorneys, accountants and other experts and
other expenses of litigation or other proceedings or of any claim, default or
assessment).

     1.13 "Master Production Records" means those records relating to the
production of Etoposide as identified in the ANDA.

     1.14 "Person" means an individual, a corporation, a partnership, an
association, a trust or other entity or organization, including a government
or political subdivision or an agency or instrumentality thereof.

     1.15 "Product" means the Etoposide injection product in vialed dosage
form currently manufactured for and sold by Immunex.  As used herein, Product
shall refer interchangeably to Etoposide injection in the 5 ml. multiple dose
vial containing 100 mg. Etoposide (NDC #58406-711-12) and the 12.5 ml.
multiple dose vial containing 250 mg. Etoposide (NDC #58406-714-18).

     1.16 "Purchase Price" shall have the meaning set forth in Section 2.2.

     1.17 "Purchased Assets" shall mean all of the (i) ANDA, (ii) Inventory,
(iii) Records and (iv) Know-How.

                                    -2-
<PAGE>

                                              CONFIDENTIAL TREATMENT REQUESTED

     1.18 "Records" means the stability reports, Master Production Records,
adverse reaction reports, material documents and correspondence with any
Governmental Authority relating to the Purchased Assets, and other records
identified on Exhibit A.

     1.19 "Termination Date" shall have the meaning set forth in Section 7.1.

     1.20 "Territory" means the United States of America including its
territories and possessions.

     1.21 "United States" means the United States of America, its territories
and possessions, the Commonwealth of Puerto Rico and the District of Columbia.

ARTICLE 2:  PURCHASE AND SALE; CLOSING

     2.1  CONVEYANCE.  On the Closing Date, subject to the terms and
conditions set forth in this Agreement, Immunex shall sell, transfer, assign,
convey and deliver to SuperGen good and marketable title to the Purchased
Assets free and clear of any Encumbrances of any kind and SuperGen shall
purchase good and marketable title to the Purchased Assets from Immunex free
and clear of any Encumbrances of any kind ("Closing Date").  Immunex shall
execute and deliver such documents of conveyance and take any other action as
may be necessary to transfer the Purchased Assets to SuperGen as set forth in
the preceding sentence.

     2.2  PURCHASE PRICE.

          (a)  In full consideration for transfer of the Purchased Assets,
SuperGen shall pay in cash $1,260,000 (the "Purchase Price") as follows:
[*] for the ANDA and [*] for the Inventory.

          (b)  The cash payments of the Purchase Price shall be made in
United States dollars by bank wire transfer in immediately available funds to
an account designated in writing by Immunex.

          (c)  The amount of the cash payment to be made on the Closing Date
is based in part upon the Inventory including no less than [*] vials of
Product as shown on Exhibit A.  Should the Inventory as actually delivered
include less than [*] vials of Product, then Immunex shall promptly upon
written notice from SuperGen, refund to SuperGen in cash the amount of (i)
[*] multiplied by the difference between [*] vials of 5 ml. Product and
the actual number of vials delivered, and (ii) [*] multiplied by the
difference between [*] vials of 12.5 ml. Product and the actual number of
vials delivered.

     In the event Immunex possess any additional Product on the Closing Date
over and above the quantities identified in Exhibit A, SuperGen shall have
the right to purchase such additional inventory at the cost of [*] per
vial for the 5 ml Product and [*] per vial for the 12.5 ml Product.

                                    -3-

<PAGE>

                                             CONFIDENTIAL TREATMENT REQUESTED


     SuperGen shall pay for all shipping costs in connection with the
delivery of the Inventory to SuperGen.

     2.3   ASSUMPTION OF LIABILITIES. SuperGen will assume at the Closing and
subsequently, in due course, pay, honor and discharge (except where it is
contesting in good faith) all liabilities and responsibilities relating to
the Purchased Assets arising after the Closing (except as set forth in
Section 6.1(a)(i)(d)), including, but not limited to all regulatory
responsibilities and obligations related to the ANDA arising after the
Closing and, with respect to the Product, all responsibilities under the
Applicable Laws relating to the use, manufacture, promotion, sale, and
distribution thereof arising after the Closing ("Assumed Liabilities").
Except as set forth in the preceding sentence, SuperGen shall not assume, and
Immunex shall retain and be responsible for, any and all liabilities and
obligations of Immunex of any kind whatsoever, including, but not limited to,
any liability relating to the Purchased Assets arising on or before the
Closing or in connection therewith, (the "Non-Assumed Liabilities").  Without
limiting the generality of the foregoing, SuperGen shall not assume (a)
liabilities of Immunex for occupation or similar taxes and related filing
fees or charges, if any, arising out of or in connection with the sale,
assignment, transfer or conveyance of the Purchased Assets hereunder to
SuperGen or (b) liabilities for federal, state, local or foreign income or
other taxes of, or due or to become due from, Immunex with respect to any
period ending on or before the Closing Date or events that occurred on or
before the Closing Date or arising out of, or resulting from the sale of the
Purchased Assets hereunder to SuperGen on or before the Closing Date.
Notwithstanding the foregoing, SuperGen will assume all liability for sales
tax on the ANDA as a result of the purchase.

     2.4   THE CLOSING.   The closing of the sale and purchase of the
Purchased Assets and the consummation of the transactions contemplated hereby
(the "Closing") shall take place at the offices of Wilson Sonsini Goodrich &
Rosati on January 15, 1997 or at such other time, date or place as the
parties may mutually agree upon in writing (the "Closing Date").  At the
Closing, the parties to this Agreement will exchange funds, certificates and
other documents specified in this Agreement.  For purposes of this Agreement
the Closing will be treated as if it occurred at 9:00 a.m. PST on the Closing
Date.

     2.5   CLOSING TRANSACTIONS.  At the Closing, and as a condition thereof
(provided any condition for the benefit of either party hereto may be waived
by such party):

           (a)  Immunex shall cause to be delivered to SuperGen the Purchased
Assets and all documents necessary to transfer, assign, convey and deliver
good and marketable title to the Purchased Assets;

           (b)  Immunex shall provide to SuperGen all necessary and
applicable notifications of change to the relevant Governmental Authorities
respecting the change in the ownership of the Purchased Assets, which
notifications shall be promptly delivered subsequent to the Closing;

           (c)  Immunex shall cause to be delivered [*] vials of Product;

           (d)  SuperGen shall deliver $1,260,000 in cash to Immunex;

                                    -4-
<PAGE>

           (e)  SuperGen will deliver such instruments of assumption and
other certificates, instruments or documents, in form and substance
reasonably acceptable to Immunex, as may be necessary to effect SuperGen's
assumption under Applicable Laws of the Assumed Liabilities;

           (f)  Each of Immunex and SuperGen shall deliver to the other party
a certificate in which an officer of each respective company certifies the
truth and accuracy of its representations and warranties set forth in Section
3 (with respect to Immunex) and Section 4 (with respect to SuperGen) as of
the Closing Date.

     2.6   Immunex reserves the right, for itself and on behalf of its
Affiliates, at any time after the Closing Date to reference the ANDA for
purposes of obtaining any registration or governmental approvals needed to
manufacture, test, sell or distribute Etoposide in any country outside of the
Territory or, subject to Section 5.5 to make Etoposide, or to have Etoposide
made in the United States solely for export and final sale outside the United
States.

ARTICLE 3:  REPRESENTATIONS AND WARRANTIES OF IMMUNEX

     Immunex hereby represents and warrants to SuperGen as follows:

     3.1   ORGANIZATION, GOOD STANDING, POWER, ETC.  Immunex is a corporation
duly organized, validly existing and in good standing under the laws of the
state of Washington and has all requisite power and authority to own, operate
and lease its properties and to carry on its business as now being conducted.
Immunex has full corporate power and authority to enter into this Agreement
and to consummate the transactions contemplated hereunder, and the execution,
delivery and performance of this Agreement and the transactions contemplated
hereby by Immunex have been duly and validly authorized by proper corporate
action, and no other proceedings on the part of Immunex are necessary to
authorize this Agreement and the transactions contemplated hereby.  This
Agreement has been duly executed and delivered by Immunex and constitutes a
legal, valid and binding obligation of Immunex enforceable against Immunex in
accordance with its terms, subject to general principles of equity and except
as enforceability hereof may be limited by applicable bankruptcy, insolvency,
reorganization or other laws of general application relating to creditors'
rights.  There are no outstanding agreements, assignments, licenses or
Encumbrances inconsistent with the provisions of this Agreement or which may
prevent or hinder Immunex from consummating the transactions contemplated by
this Agreement or may prevent or hinder SuperGen from sponsoring the ANDA.

     3.2   NO CONFLICT.  Neither the execution and delivery of this Agreement
nor the consummation of the transactions contemplated hereby will: (i)
conflict with the articles of incorporation or by-laws of Immunex; (ii)
violate any order, writ, injunction or decree applicable to Immunex; (iii)
violate any provisions of laws, rules or regulations to which Immunex is
subject; (iv) violate, conflict with or result in any breach of or default
under any mortgage, indenture, contract, agreement, license, permit,
instrument or trust to which Immunex is a party or by which its properties
are bound; or (v) result in the creation or imposition of any Encumbrance of
any kind whatsoever upon, or give to any person other than SuperGen any
interest or right in the Purchased

                                    -5-
<PAGE>

Assets or give any right of acceleration, termination or cancellation in or
with respect to, any of the ANDA or the rights of SuperGen to be the sponsor
thereof.

      3.3   CONSENTS AND APPROVALS.  Immunex has obtained all necessary
consents, approvals, orders or authorizations of, and has performed all
necessary registrations, declarations or filings with any Governmental
Authority required by or with respect to Immunex in connection with the
execution and delivery of this Agreement by Immunex or the consummation by
Immunex of the transactions contemplated hereby.  Immunex is conducting, and
has conducted, its business and operations as it relates directly or
indirectly to the Purchased Assets in compliance in all material respects
with all governmental laws, rules and regulations applicable thereto and is
not in violation or default in any material respect under any statute,
regulation, order, decree or governmental authorization applicable to it or
any of its properties or business as presently conducted or proposed to be
conducted as it relates directly or indirectly to the Purchased Assets,
including without limitation laws, rules and regulations administered or
issued by the FDA and any environmental laws, rules and regulations.  Immunex
is not subject to any order or consent decree of any court or administrative
body that relates in any way, directly or indirectly, to the Purchased
Assets.

     3.4   PURCHASED ASSETS.  Immunex has full right, title and interest to,
and at the Closing will sell, convey, assign, transfer and deliver to
SuperGen good title to all Purchased Assets.  The Purchased Assets are free
and clear of any Encumbrance of any party.  There are no material problems or
defects in any of the Purchased Assets which would directly or indirectly
adversely affect such Purchased Assets or SuperGen's ability to sell Product
after the Closing or, as a direct or indirect result of such defects, would
render the Product unmarketable for the purposes for which they were
intended.  All material adverse experiences associated with the Immunex
labeled product and known to Immunex are included in the ANDA.  To the best
of Immunex's knowledge, there is no infringement by any third party of its
title to the Purchased Assets.

     3.5   LEGAL PROCEEDINGS.  There are no adverse third party actions or
claims pending against Immunex  in any court or by or before any Governmental
Authority with respect to the Purchased Assets.  There are no other actions,
suits, proceedings, claims or, to the best knowledge of Immunex,
investigations pending against Immunex, nor has Immunex received notice of
any of the foregoing, with respect to the transactions contemplated hereby or
materially affecting the value of the Purchased Assets or which, if adversely
determined, would prevent Immunex from consummating the transactions
contemplated hereby.  There is no reason that could preclude SuperGen from
marketing and selling the Purchased Assets in the Territory after the Closing.

     3.6   INVENTORY.  As of the Closing Date (i) all the Inventory is in
good and merchantable condition; (ii) all of the Inventory was prepared in
compliance with current good manufacturing practice regulations for
pharmaceuticals, and (iii) all finished Inventory which has been released
meets all applicable specifications and legal requirements and may be
lawfully sold in the Territory. The expiration date on all such Inventory is
as set forth on Exhibit A.

                                    -6-
<PAGE>

     3.7   TAXES.  Immunex has duly paid all taxes and other governmental
charges, if any, due and payable upon the Purchased Assets and any income or
sales tax, if any, relating to the Purchased Assets prior to the Closing
Date. Neither the Internal Revenue Service nor any other taxing authority has
in the past asserted or is now asserting or, to the best knowledge of
Immunex, is threatening to assert against Immunex, any deficiency or claim
for additional taxes or interest thereon or penalties in connection therewith
with respect to the Purchased Assets.

     3.8   RECORDS.  Immunex has delivered to SuperGen true and complete
copies of all Records. The Records include all documents (other than
marketing projections and routine correspondence between Immunex and its
Affiliates regarding the Product) of any kind whatsoever which are directly
or indirectly material to the Purchased Assets.

     3.9   AGREEMENTS.  There are no outstanding contracts, leases,
instruments, obligations, commitments, understandings and agreements, whether
written or oral, to which Immunex is a party and to which the Purchased
Assets will be subject subsequent to the Closing. Immunex has no material
agreement with any third party which will obligate SuperGen to make any
payments to such third parties with respect to any of the Purchased Assets.

     3.10  FDA MATTERS.  The Product now being commercially distributed by
Immunex in the Territory meets the applicable legal requirements of the
applicable jurisdiction in all material respects and all requisite
governmental approvals have been duly obtained and are in full force and
effect.  There is no action or proceeding by the FDA or any other
Governmental Authority, including, but not limited to, recall procedures,
pending or, to the knowledge of Immunex, threatened against Immunex relating
to safety or efficacy of any of the Purchased Assets.

     3.11  FULL DISCLOSURE.  No representation, warranty or statement of
Immunex in this Agreement contains or will contain at the Closing Date any
untrue statement of a material fact or omits or will omit to state a material
fact necessary in order to make the statements contained herein, in light of
the circumstances under which made, not misleading.

ARTICLE 4:  REPRESENTATIONS AND WARRANTIES OF SUPERGEN

     SuperGen hereby represents and warrants to Immunex as follows:

     4.1   CORPORATE ORGANIZATION.  SuperGen is a corporation duly organized,
validly existing and in good standing under the laws of California.  SuperGen
has the requisite power and authority to own, operate and lease its
properties and carry on its business as now being conducted.

     4.2   AUTHORITY RELATIVE TO THIS AGREEMENT.  SuperGen has the requisite
corporate power and authority to execute and deliver this Agreement and to
consummate the transactions contemplated hereby.  The execution and delivery
by SuperGen of this Agreement and the consummation by SuperGen of the
transactions contemplated hereby have been duly authorized by all necessary
corporate action on the part of SuperGen and no other corporate proceeding is
necessary

                                    -7-
<PAGE>

for the execution and delivery of this Agreement, the performance by SuperGen
of its obligations hereunder and the consummation by SuperGen of the
transactions contemplated hereby.  This Agreement has been duly executed and
delivered by SuperGen and constitutes a legal, valid and binding obligation
of SuperGen, enforceable against SuperGen in accordance with its terms,
except as the same may be limited by bankruptcy, insolvency, moratorium,
reorganization or other laws of general applicability relating to or
affecting the enforcement of creditor's rights and general principles of
equity.

     4.3   NO CONFLICT.  The execution, delivery and performance of this
Agreement by SuperGen shall not (i) conflict with or result in any breach of
any provision of the certificate of incorporation or bylaws of SuperGen; or
(ii) violate any order, writ, injunction, decree, or any statute, rule or
regulation applicable to SuperGen or its Affiliates or any of its properties
or assets.

     4.4   FINANCING.  SuperGen has sufficient funds available to purchase
the Purchased Assets and to pay all related fees and expenses for which
SuperGen is responsible pursuant to the terms hereof.

     4.5   NO OTHER REPRESENTATIONS OR WARRANTIES.  Except for the
representations and warranties of SuperGen expressly set forth in this
Agreement, neither SuperGen nor any other Person makes any other express or
implied representation or warranty on behalf of SuperGen.

ARTICLE 5:  COVENANTS

     Immunex covenants and agrees with SuperGen and SuperGen covenants and
agrees with Immunex as follows:

     5.1   POST-CLOSING ORDERS.  After the Closing Date, Immunex agrees to
forward to SuperGen all unfilled orders for Product received after the
Closing Date.

     5.2   SALE OF THE PRODUCT.  Immunex hereby agrees that SuperGen shall
have the right to sell in the Territory any Inventory bearing the "Immunex"
trademark which may be included in the Purchased Assets.  SuperGen agrees to
maintain any such Inventory under conditions required by the ANDA and any
other applicable laws and regulations in order to assure that the Product
meets all approved specifications at the time of distribution.

     5.3   FURTHER ASSURANCES.  From time to time, without further
consideration, each party, at its own expense, shall execute and deliver such
documents to the other party and shall take such further actions as such
other party may reasonably request in order more effectively to consummate
the transactions contemplated hereby.  In addition, without limiting and
subject to the indemnification set forth in Section 6.1(b), Immunex agrees
that it will reasonably cooperate, at SuperGen's request, in the event of any
litigation regarding the Purchased Assets, provided that SuperGen agrees to
pay Immunex's out-of-pocket expenses relating thereto.

                                    -8-
<PAGE>

     5.4   NOTICES OF CERTAIN EVENTS.  Immunex and SuperGen covenant and
agree that, pending the Closing, each shall notify the other of any fact or
condition, including but not limited to any notice or other communication
from any Person alleging that the consent of such Person is or may be
required in connection with the transactions contemplated by this Agreement,
any notice or communication from any Governmental Authority in connection
with the Purchased Assets or the transactions contemplated by this Agreement,
or, with respect to SuperGen, any condition which may effect its ability to
pay the Purchase Price, which could delay or otherwise prevent the Closing.

     5.5   IMMUNEX'S COVENANT NOT TO COMPETE.

           (a)  In furtherance of the transactions contemplated by this
Agreement and in order to secure the interests of the parties hereto, Immunex
agrees that it will not, for a period of six years from the Closing Date, for
any reason whatsoever, directly or indirectly, for itself or on behalf of or
in conjunction with any other Person sell Product anywhere in the Territory
or have any ownership interest in, or participate in the financing,
operation, management or control of any Person selling Product in the
Territory or enter into any partnership, joint venture or similar
collaborative arrangement with any Person to sell Product in the Territory,
or transfer Product to a third person with the intent to sell Product in the
Territory.  Notwithstanding the foregoing, in the event that Immunex is
acquired by a company that prior to the time of the acquisition is in the
business of selling the Etoposide, the acquisition of Immunex by such company
(and such parent company's subsequent continued sale of the Etoposide) shall
not constitute a breach of this covenant not to compete.

           (b)  It is expressly understood and agreed that, if any of the
agreements contained in this Section 5.5 are for any reason found to be
unreasonably broad, oppressive or unenforceable in an action, suit or
proceeding before any federal or state court, such court (i) shall narrow the
covenant not to compete or shall otherwise endeavor to reform the scope of
such agreements in order to ensure that the application thereof is not
unreasonably broad, oppressive or unenforceable and (ii) to the fullest
extent permitted by law, shall enforce such agreements as so reformed.

           (c)  All of the covenants in this Section 5.5 shall be construed
as an agreement independent of any other provision in this Agreement, and the
existence of any claim or cause of action of Immunex against SuperGen,
whether predicated on this Agreement or otherwise, shall not constitute a
defense to the enforcement by SuperGen of such covenants.  It is specifically
agreed that the period of six years stated at the beginning of this Section
5.5, during which the agreements and covenants of Immunex made in this
Section 5.5 shall be effective, shall be computed by excluding from such
computation any time during which Immunex is found by a court of competent
jurisdiction to have been in violation of any provision of this Section 5.5.
The covenants contained in Section 5.5 shall not be affected by any breach of
any other provision hereof by an party hereto and shall have no effect if the
transactions contemplated by this Agreement are not consummated.

           (d)  Immunex and SuperGen hereby agree that the covenants set
forth in this Section 5.5 are a material and substantial part of the
transactions contemplated by this Agreement.

                                    -9-
<PAGE>

           (e)  Because of the difficulty of measuring economic losses to
SuperGen as a result of a breach of the restrictive covenants set forth in
this Section 5.5, and because of the immediate and irreparable damage that
would be caused to SuperGen for which monetary damages would not be a
sufficient remedy, it is hereby agreed that in addition to all other remedies
that may be available to SuperGen at law or in equity, SuperGen shall be
entitled to specific performance and any injunctive or other equitable relief
as a remedy for any breach or threatened breach of the aforementioned
restrictive covenants.

ARTICLE 6:  INDEMNIFICATION

     6.1   INDEMNIFICATION

           (a)  INDEMNIFICATION BY IMMUNEX.  Immunex covenants and agrees to
indemnify, defend, protect and hold harmless SuperGen and its officers,
directors, employees, stockholders, assigns, successors and Affiliates
(individually, a "SuperGen Indemnified Party" and collectively, "SuperGen
Indemnified Parties") from, against and in respect of:

                (i)  all Losses suffered, sustained, incurred or paid by any
SuperGen Indemnified Party in connection with, resulting from or arising out
of or relating to, directly or indirectly:

                     (a)  any breach of any representation or warranty of
Immunex set forth in this Agreement or any certificate, document or
instrument delivered by or on behalf of Immunex in connection herewith;

                     (b)  any nonfulfillment of any covenant or agreement on
the part of Immunex in this Agreement;

                     (c)  claims or causes of actions (including but not
limited to for injuries or death of persons or damage to property) relating
in any way to the Purchased Assets arising prior to the Closing, including
but not limited to claims or causes of action relating to the manufacture,
promotion, use, sale or distribution of Product;

                     (d)  claims or causes of actions (including but not
limited to for injuries or death of persons or damage to property) arising
subsequent to the Closing relating to the manufacture of Product (including
Inventory) prior to the Closing;

                     (e)  any negligent or reckless actions by Immunex or its
employees in connection with the fulfillment of its obligations set forth in
this Agreement;

                     (f)  any other Non-Assumed Liabilities;



                                    -10-
<PAGE>

                     (g)  non-compliance with the terms and conditions of any
bulk sales laws with respect to the transactions contemplated by this
Agreement; and

                (ii) any and all Losses arising from the foregoing or to the
enforcement of this Section 6.1(a).

           (b)  INDEMNIFICATION BY SUPERGEN.  SuperGen covenants and agrees
to indemnify, defend, protect and hold harmless Immunex and its officers,
directors, employees, stockholders, assigns, successors and Affiliates
(individually, a "Immunex Indemnified Party" and collectively, the "Immunex
Indemnified Parties") from, against and in respect of:

                (i)  all Losses suffered, sustained, incurred or paid by any
Immunex Indemnified Party in connection with, resulting from or arising out
of or relating to, directly or indirectly:

                     (a)  any breach of any representation or warranty of
SuperGen set forth in this Agreement or any certificate or other writing
delivered by SuperGen in connection herewith;

                     (b)  any nonfulfillment of any covenant or agreement on
the part of SuperGen set forth in this Agreement;

                     (c)  subject to Section 6.1(a)(i)(d), SuperGen's
promotion, use, sale or distribution of Product after the Closing Date; and

                     (d)  any other Assumed Liability.

                (ii) any and all Losses arising from the foregoing or to the
enforcement of this Section 6.1(b).

           (c)  All Claims for indemnification under this Section 6.1 shall
be asserted and resolved as follows:

                (i)   Any party that may be entitled to indemnification under
this Agreement, (an "Indemnified Party") shall send a Claim Notice (as
defined below) to the party obligated to indemnify it (an "Indemnifying
Party") with reasonable promptness upon becoming aware of any claim or other
facts upon which a claim for indemnification might be based.  If the
Indemnifying Party does not notify the Indemnified Party within 30 days from
the date of receipt of such Claim Notice that the Indemnifying Party disputes
such claim, the amount of such claim shall be conclusively deemed a liability
of the Indemnifying Party hereunder.  In case the Indemnifying Party shall
object in writing to any claim made in accordance with this Section 6.1(c),
the Indemnified Party shall have fifteen (15) days to respond in a written
statement to the objection of the Indemnifying Party.  If after such fifteen
(15) day period there remains a dispute as to any claims, the parties shall
attempt in good faith for sixty (60) days to agree upon the rights of the
respective parties with respect to each of such

                                    -11-
<PAGE>

claims.  If the parties should so agree, a memorandum setting forth such
agreement shall be prepared and signed by both parties.  If no such agreement
can be reached by Immunex or SuperGen, then either party may, by written
notice to the other, demand arbitration of the matter in accordance with the
arbitration provision set forth in Section 8.10.

                (ii)  In the event that any claim for which an Indemnifying
Party would be liable to an Indemnified Party hereunder is asserted against
an Indemnified Party by a third party, the Indemnified Party shall with
reasonable promptness notify the Indemnifying Party of such claim, including
a copy of the claim made if the claim was made in writing, specifying the
nature of such claim and the amount or the estimated amount thereof to the
extent then feasible (which estimate shall not be conclusive of the final
amount of such claim) (the "Claim Notice").  The Indemnifying Party shall
have 30 days from the receipt of the Claim Notice (the "Notice Period") to
notify the Indemnified Party (i) whether or not the Indemnifying Party
disputes the Indemnifying Party's liability to the Indemnified Party
hereunder with respect to such claim and (ii) if the Indemnifying Party does
not dispute such liability, whether or not the Indemnifying Party desires, at
the sole cost and expense of the Indemnifying Party, to defend against such
claim, provided that the Indemnifying Party is hereby authorized (but not
obligated) prior to and during the Notice Period to file any motion, answer
or other pleading and to take any other action which the Indemnifying Party
shall deem necessary or appropriate to protect the Indemnifying Party's
interests.  In the event that the Indemnifying Party notifies the Indemnified
Party within the Notice Period that the Indemnifying Party does not dispute
the Indemnifying Party's obligation to indemnify hereunder and desires to
defend the Indemnified Party against such claim and except as hereinafter
provided, the Indemnifying Party shall have the right to defend by
appropriate proceedings, which proceedings shall be diligently settled or
prosecuted by the Indemnifying Party to a final conclusion; PROVIDED that,
unless the Indemnified Party otherwise agrees in writing, the Indemnifying
Party may not settle any matter (in whole or in part) unless such settlement
includes a complete and unconditional release of the Indemnified Party.  If
the Indemnified Party desires to participate in, but not control, any such
defense or settlement the Indemnified Party may do so at the Indemnified
Party's sole cost and expense.  If the Indemnifying Party elects not to
defend the Indemnified Party against such claim, whether by failure of the
Indemnifying Party to give the Indemnified Party timely notice as provided
above or otherwise, then the Indemnified Party, without waiving any rights
against the Indemnifying Party, may settle or defend against any such claim
in the Indemnified Party's sole discretion and the Indemnified Party shall be
entitled to recover from the Indemnifying Party the amount of any settlement
or judgment and, on an ongoing basis, all indemnifiable costs and expenses of
the Indemnified Party with respect thereto, including interest from the date
such costs and expenses were incurred.

                (iii)  Nothing herein shall be deemed to prevent an
Indemnified Party from making a claim, and an Indemnified Party may make a
claim hereunder, for potential or contingent claims or demands provided the
Claim Notice sets forth the specific basis for any such potential or
contingent claim or demand to the extent then feasible and an Indemnified
Party has reasonable grounds to believe that such a claim or demand may be
made.

                (iv)  The Indemnified Party's failure to give reasonably
prompt notice to the Indemnifying Party of any actual, threatened or possible
claim or demand which may give rise to a

                                    -12-
<PAGE>

right of indemnification hereunder shall not relieve the Indemnifying
Party of any liability which the Indemnifying Party may have to the
Indemnified Party unless the failure to give such notice materially and
adversely prejudiced the Indemnifying Party.

     6.2   INDEMNIFICATION FOR BROKERAGE CLAIMS.  Immunex and SuperGen each
represents that no broker or finder has been used in connection with the
transactions contemplated by this Agreement and Immunex and SuperGen shall
mutually indemnify the other against any claim for brokerage or like
commission arising from each other's conduct or alleged conduct.

     6.3   SURVIVAL OF REPRESENTATIONS, WARRANTIES AND COVENANTS.  All
representations, warranties and covenants (except for Section 5.5 which shall
survive for six years) contained in this Agreement shall survive for a period
of four years from the date hereof and thereafter shall be of no force or
effect. Any claim for indemnification with respect thereto must be asserted
by written notice to the Indemnifying Party prior to such date.

ARTICLE 7:  TERMINATION, AMENDMENT AND WAIVER

     7.1   TERMINATION.  This Agreement may be terminated at any time prior
to the Closing Date:

           (a)   by mutual written consent of SuperGen and Immunex;

           (b)   by SuperGen or Immunex if the Closing shall not have
occurred on or prior to February 1, 1997, provided, however, that a party
shall not have the right to terminate under this Section 7.1(b) if such
party's (or such party's Affiliates) failure to fulfill any obligation under
this Agreement has been the cause of, or resulted in the failure of the
Closing to occur on or before such date of any liability of such party to the
other party hereunder for such failure;

           The date on which this Agreement is terminated pursuant to any of
the foregoing subsections of this Section 7.1 is herein referred to as the
"Termination Date."

     7.2   EFFECT OF TERMINATION.  Upon the termination of this Agreement
pursuant to Section 7.1, this Agreement shall forthwith become null and void,
except that nothing herein shall relieve any party from liability for breach
of this Agreement prior to such termination.

ARTICLE 8:  GENERAL PROVISIONS

     8.1   PUBLIC STATEMENTS.  Except as may be required to comply with the
requirements of applicable law, no press release or similar public
announcement or communication will be made or caused to be made by the
parties concerning the execution and delivery of this Agreement or the
consummation of the transactions contemplated hereby, unless specifically
approved in advance by the other party hereto.

                                    -13-
<PAGE>

     8.2   NOTICES.  All notices and other communications hereunder shall be
in writing and shall be deemed to have been duly given if delivered
personally, mailed by reputable overnight courier or certified mail (return
receipt requested) or sent by telecopier (confirmed thereafter by certified
mail) to the parties at the following addresses or at such other addresses as
shall be specified by the parties by like notice:

           (a)    if to Immunex:

                  51 University Street
                  Seattle, Washington 98101
                  Attention:  Director of New Business
                  Telecopier Number:  [206] 587-0606

                  with a copy to:

                  Law Department
                  51 University Street
                  Seattle, Washington 98101
                  Attention:  General Counsel
                  Telecopier Number:  [206] 233-0644

            (b)   if to SuperGen addressed to:

                  SuperGen, Inc.
                  6450 Hollis Street
                  Emeryville, California  94608
                  Attention:  Chief Executive Officer
                  Telecopier Number: (510) 655-1098

                  with a copy to:

                  John V. Roos, Esq.
                  Wilson Sonsini Goodrich & Rosati
                  Two Palo Alto Square
                  Palo Alto, California 94306

     Notice so given shall (in the case of notice so given by mail) be deemed
to be given and received on the third calendar day after mailing or the next
business day if sent by a reputable overnight courier and (in the case of
notice so given by telecopier or personal delivery) on the date of actual
transmission or (as the case may be) personal delivery.

     8.3   RETURNS. Any returns of the Product sold before the Closing Date
in the Territory, whether returned to SuperGen or Immunex, shall be for the
account of Immunex.  Any returns of the Product sold after the Closing Date
in the Territory, whether returned to SuperGen or Immunex, shall

                                    -14-
<PAGE>

be for the account of SuperGen.  Any returns of the Product received by
Immunex shall be promptly destroyed by Immunex, and Immunex shall notify
SuperGen in writing within 30 days of its receipt and destruction of such
returns with respect to Product owned by SuperGen.  Any returns of the
Product received by SuperGen shall be promptly destroyed by SuperGen, and
SuperGen shall notify Immunex in writing within 30 days of its receipt and
destruction of such returns with respect to Product owned by Immunex.

     8.4   WAIVER.  Any waiver must be explicitly in writing.  A waiver of
any breach or failure to enforce any of the terms or conditions of this
Agreement shall not in any way affect, limit, or waive a party's rights at
any time to enforce strict compliance thereafter with every term or condition
of this Agreement.

     8.5   PARTIES IN INTEREST.  This Agreement shall not run to the benefit
of or be enforceable by any person other than a party to this Agreement and,
subject to Section 8.8, its successors and assigns provided, however, the
persons entitled to indemnification under Article 6 shall be beneficiaries of
such provisions.

     8.6   ENTIRE AGREEMENT; GOVERNING LAW; MISCELLANEOUS.  This Agreement
(including the documents and instruments referred to herein) constitutes the
entire agreement and supersedes all other prior agreements and undertakings,
both written and oral, among the parties, or any of them, with respect to the
subject matter hereof; is not intended to confer upon any other person any
rights or remedies hereunder; and shall be governed in all respects,
including validity, interpretation and effect, by the internal laws of the
State of California without giving effect to the principles of conflicts of
laws thereunder.  This Agreement may be executed in one or more counterparts
which together shall constitute a single agreement.  If any provision of this
Agreement shall be held to be illegal, invalid or unenforceable under any
applicable law, then such contravention or invalidity shall not invalidate
the entire Agreement.  Such provision shall be deemed to be modified to the
extent necessary to render it legal, valid and enforceable, and if no such
modification shall render it legal, valid and enforceable, then this
Agreement shall be construed as if not containing the provision held to be
invalid, and the rights and obligations of the parties shall be construed and
enforced accordingly.

     8.7   EXPENSES.  All expenses, including the fees of any attorneys,
accountants, investment bankers or others engaged by a party, incurred in
connection with this Agreement and the transactions contemplated hereby,
shall be paid by the party incurring such expenses whether or not the
transactions contemplated by this Agreement are consummated.

     8.8   ASSIGNABILITY AND AMENDMENTS.  This Agreement may not be assigned
by either party without the prior written consent of the other party, which
consent shall not be unreasonably withheld, except that, subsequent to the
Closing Date, either party may assign this Agreement to any of its
Affiliates, provided, that such Affiliates agree to be bound by the
provisions of this Agreement.  No such assignment will relieve the assigning
party of any of its liabilities hereunder. This Agreement cannot be altered
or otherwise amended except pursuant to an instrument in writing signed by
each of the parties.

                                    -15-
<PAGE>

     8.9   CONFIDENTIALITY.  Each party hereby agrees, and shall cause its
Affiliates to agree, that after the Closing Date, such party and its
Affiliates shall hold in confidence and not disclose to any third Person, nor
use for its own benefit any confidential or proprietary information of the
other party or its Affiliates that is disclosed to or discovered by such
party or its Affiliates in connection with the transactions contemplated
hereby, unless (i) such information becomes known to the public generally
through no fault of such party or its Affiliates or (ii) disclosure is
required by law or the order of any Governmental Authority under color of law.

     8.10  ARBITRATION. All disputes or controversies (whether of law or
fact) of any nature whatsoever arising from or relating to this Agreement and
the transactions contemplated hereby shall be decided by the American
Arbitration Association in accordance with the rules and regulations of that
association. The arbitrators shall be selected as follows:  SuperGen and
Immunex shall, within 30 days of the date of demand by either party for
arbitration, each select one independent, qualified arbitrator and the two
arbitrators so selected shall select the third arbitrator within 30 days
after their appointment as party arbitrators.  Each party reserves the right
to object to any individual arbitrator who shall be employed by or affiliated
with a competing organization. In the event objection is made, the American
Arbitration Association (the "Association") shall resolve any dispute
regarding the propriety of an individual arbitrator acting in that capacity.
The parties shall each bear the expenses of the arbitrator chosen by it, and
shall bear one-half the expenses of the independent arbitrator.  Hearings in
the proceeding shall commence within 120 days of the selection of the neutral
arbitrator.  Arbitration shall take place in Alameda County, California.  At
the request of either party, arbitration proceedings will be conducted
confidentially; in such case all documents, testimony and records shall be
received, heard and maintained by the arbitrators in confidence under seal,
available for the inspection only by the Association, SuperGen and Immunex
and their respective attorneys and their respective experts who shall agree
in advance and in writing to receive all such information confidentially and
to maintain such information in confidence.  The arbitrators, who shall act
by majority vote, shall be able to decree any and all relief of an equitable
and legal nature, including but not limited to such relief as a temporary
restraining order, a temporary and/or a permanent injunction, and shall also
be able to award damages, with or without an accounting and costs.  The
decree or award rendered by the arbitrators may be entered as a final and
binding judgment in any court having jurisdiction thereof.  Reasonable notice
of the time and place of arbitration shall be given to all persons, other
than the parties, as shall be required by law, in which case such persons or
those authorized representatives shall have the right to attend and/or
participate in all the arbitration hearings in such manner as the law shall
require.  The resolution of conflicts procedures set forth in this Section
8.10 are the parties' sole and exclusive methods for resolving disputes
arising out of this Agreement.  Except as expressly set forth above, the
parties agree to waive all rights to commence any action in law or equity
arising out of this Agreement.

                                    -16-
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
executed as of the date first above written.

                                 IMMUNEX CORPORATION


                                 By: /s/ Edward V. Fritzky
                                    ----------------------------------------
                                      Name:   Edward V. Fritzky
                                      Title:  Chairman, Chief Executive Officer


                                 SUPERGEN INC.


                                 By: /s/ Hank Settle
                                    ----------------------------------------
                                      Name:  Hank Settle
                                      Title: Chief Financial Officer



                                    -17-
<PAGE>

                                             CONFIDENTIAL TREATMENT REQUESTED

                                    EXHIBIT A

                                    INVENTORY


PRODUCT:
                                                               Expiration
    NDC #          Description         Lot #     Quantity         Date
------------   -----------------      -------   -----------    ----------

58406-711-12   5ml multiple dose      EP10020      [*]            02/98
                                      EP10030      [*]            02/98
                                      EP10050      [*]            02/98
                                      EP10060      [*]            03/98
                                      EP10070      [*]            03/98
                                      EP10080      [*]            03/98
                                      EP10090      [*]            03/98

                                        Total      [*]


58406-714-18   12.5ml multiple dose   EP20020      [*]            02/98
                                      EP20030      [*]            02/98

                                        Total      [*]


                                     RECORDS

Signed Application Form FDA 356h

Basis for ANDA Submission

Patent Certification and Exclusivity Statement

Comparison Between Generic Drug and Reference Listed Drug:

     1.   Conditions of Use

     2.   Active Ingredient(s)

     3.   Route of Administration, Dosage Form, and Strength


<PAGE>

Labeling

Bioavailability/Bioequivalence

     1.   IN VIVO Study Protocol(s) (N/A)

     2.   IN VIVO Study (N/A)

     3.   Request for Waiver of In Vivo Study(ies)

     4.   IN VITRO Dissolution Data (N/A)

     5.   Formulation Data (Comparison of all Strengths)

Components and Composition Statements

Raw Materials Controls

     1.   Active Ingredient(s)

          a.   Synthesis Listing Manufacturer/Supplier (Type II
               DMF authorization Letters)

          b.   Certificate(s) of Analysis specifications and test
               results from Drug Substance Manufacturer(s) (Including Material
               Safety Data Sheet)

          c.   Testing specifications and data (Lederle Monograph
               and COAs)

          d.   Spectra and Chromatograms for reference standards
               and test samples

          e.   Approved application for bulk antibiotic

     2.   Inactive Ingredients

          a.   Testing Specifications (Lederle Monographs)

          b.   Suppliers' & Lederle's Certificates of Analysis
               (Specifications and Results)

     3.   Standard Operating Procedures (SOPs)

          a.   Qualification of vendors

          b.   Acceptance Criteria

          c.   Retest Schedule


<PAGE>

          d.   Storage

Description of Manufacturing Facility

     1.   Full address(es) of the Facility(ies) for the Manufacturing
          Process, Testing, and Stability Testing

     2.   Brief Description of the Facility Including Sito Plan

     3.   eGMP Certification

     4.   Debarment Statement

Outside Firms Including Contract Testing Laboratories

     1.   Full Address

     2.   Functions

     3.   cGMP Certification/GLP (DMF Letters)

Manufacturing and Processing Instructions

     1.   Description of Manufacturing Process
          -    Aseptic Validation Package
          -    Process Flow Chart

     2.   Blank Batch Record(s) for Intended Production Runs with Equipment
          Specified

     3.   Reprocessing Statement

In-Process Controls

     1.   Copy of Executed Batch Record (AADA/Three Batches) with
          Equipment Specified, Including Packaging Records Reconciliation and
          Label Reconciliation

     2.   In Process

          a.   Sampling Plans and Testing Procedures

          b.   Specifications and Data (Including In-Process Sampling Report)

Packaging and Labeling Procedures

<PAGE>

Container

     1.   Summary of Container/Closure System

     2.   Components Specification and Test Data

          a.   Packaging Specification

          b.   Type III DMF References

     3.   Packaging Configurations and Sizes

     4.   Container/Closure Testing

Controls for the Finished Dosage Form

     1.   Sampling Plans and Test Procedures

     2.   Testing Specifications and Data (Including Monograph and
          COAs)

Analytical Methods (Three Additional Separate Bound Copies if the Drug Substance
and/or Drug Product are not USP Articles)

     1.   Methods for Drug Substance

          a.   Method Validation

          b.   Test Specifications and Data

     2.   Methods for Drug Product

          a.   Method Validation (Including APRs)

          b.   Stability-indicating test data of samples
               undergone various stress conditions

          c.   Test Specifications and Data

Stability of Finished Dosage Form

     1.   Protocol

     2.   Post Approval Commitments

     3.   Expiration Dating Period


<PAGE>

     4.   Stability Data Submitted

Control Numbers

     1.   For Raw Materials

     2.   For Production Batches

Samples - Sample Availability and Identification of:

     1.   Drug Substance

     2.   Finished Dosage Form

Environmental Impact Analysis Statement

Other

     1.   Reference to Previously Submitted Information (N/A)

     2.   Literature Publication for Which English Translation is
          Submitted (N/A)

     3.   Letters of Authorization (N/A)

     4.   DEA Statement (N/A)