<PAGE>

                                                                   EXHIBIT 10.18

                                                        ----------------
                                                        REDACTED VERSION
                                                        ----------------

                                 EXHIBIT 10.18

                                       TO

                               ICOS CORPORATION'S

                                   FORM 10-K

                               FOR THE YEAR ENDED

                               DECEMBER 31, 1996



          "[    *    ]" = omitted, confidential material, which material has
been   separately filed with the Securities and Exchange Commission pursuant to
a request for confidential treatment.
<PAGE>

                            SHAREHOLDERS' AGREEMENT

          THIS SHAREHOLDERS' AGREEMENT ("Agreement") is made and entered into at
Bothell, Washington, U.S.A. this 18th day of December, 1996, by and among ICOS
CORPORATION, a Delaware corporation ("ICOS"), SUNTORY LIMITED, a Japanese
corporation ("Suntory"), and SUNCOS CORPORATION, a Delaware corporation
("Company").

                                    RECITALS

          A.    ICOS has conducted research, has developed and possesses certain
existing proprietary patent rights, technical information, technology and know-
how relating to molecular biology [   *   ].

          B.    Suntory and ICOS believe that the aforementioned patent rights,
information, technology and know-how will have important application to the
development of [   *   ].

          C.    Suntory and ICOS desire to form the Company to engage in the
development, manufacture, production and worldwide commercial sale of platelet-
activating factor acetylhydrolase [   *   ].

          D.    Suntory and ICOS believe that a joint business effort between
them dedicated to such purposes would be of mutual benefit to the accomplishment
thereof and that the compatibility between ICOS and Suntory is such that
substantial economic returns may be gained by each through cooperative effort.

          E.    ICOS intends to [   *   ] in the Field of Activity (as defined
in Paragraph 1.03 below) in consideration of the issuance to ICOS of capital
stock in the Company as more fully set forth herein.

          F.    Suntory intends to contribute cash to the Company in
consideration of the issuance to Suntory of capital stock in the Company as more
fully set forth herein.


          *   Confidential Treatment Requested
<PAGE>

          G. The simultaneous transfers and resultant issuances contemplated in
Recitals E and F above are intended to qualify as a tax-free incorporation of
the Company pursuant to Section 351 of the Internal Revenue Code of 1986, as
amended.

          H. It is the desire of Suntory and ICOS to cooperate in other mutually
agreeable areas of business interest.

        NOW, THEREFORE, it is hereby agreed as follows:

1.      CERTAIN DEFINITIONS

        As used in this Agreement, the following terms shall have the following
meanings:

        1.01  COMMON STOCK

        The term Common Stock shall mean the duly authorized common stock of
        the Company having a par value of $.0001 per share.

        1.02  PAF-AH

        The term PAF-AH shall mean platelet-activating factor acetylhydrolase
[ * ].

        1.03  FIELD OF ACTIVITY

        The term Field of Activity shall mean [ * ].

        1.04  BACKGROUND TECHNOLOGY

        The term Background Technology shall mean [ * ].

        1.05  PAF-AH TECHNOLOGY

        The term PAF-AH Technology shall mean [ * ].

        1.06  DEVELOPMENT PROGRAM

        The term Development Program, as more fully set forth in the
Development and Supply Agreement attached hereto as Exhibit B ("Development and
Supply Agreement"), shall mean [ * ].



        *   Confidential Treatment Requested

                                       2
<PAGE>

        1.07  PAF-AH ORGANISMS

        The term PAF-AH Organisms shall mean [   *   ].


        1.08  PARTY

        The term Party shall mean Suntory, ICOS or the Company, as the context
shall indicate, or, when used in the plural, Suntory, ICOS and the Company, as
the context shall indicate.

2.      FORMATION

        2.01  FORMATION

        On or before the Closing Date (as defined in Paragraph 3 below),
Suntory and ICOS shall establish, or cause to be established, "Suncos
Corporation" which shall be a corporation organized under the laws of the State
of Delaware.  Immediately after its formation, Suncos Corporation shall become a
Party to this Agreement.

        2.02  NAME

        The corporate designation of the Company shall be "Suncos Corporation"
or such other name as may be mutually agreed to by Suntory and ICOS.

        2.03  PRINCIPAL OFFICE

        The principal office and place of business of the Company shall be
located at 1209 Orange Street, Wilmington, Delaware, U.S.A., or at such other
place as may be mutually agreed to by Suntory and ICOS.

        2.04  ARTICLES OF INCORPORATION

        The Articles of Incorporation of the Company ("Articles") shall be as
attached hereto as Exhibit C, as may be amended from time to time as may be
mutually agreed to by Suntory and ICOS.


          *   Confidential Treatment Requested


                                       3
<PAGE>

        2.05   BYLAWS

        The Bylaws of the Company ("Bylaws") shall be as attached hereto as
Exhibit D, as may be amended from time to time as may be mutually agreed to by
Suntory and ICOS.

        2.06   BUSINESS PURPOSE

The business of the Company shall be to engage in the development, manufacture,
production and sale of PAF-AH Products [   *   ] in the Field of Activity and
to [   *   ] such PAF-AH Technology in the Field of Activity for [   *   ]
including, but not limited to, the [   *   ] of such PAF-AH Technology by mutual
agreement of Suntory and ICOS, and to do all things necessary, appropriate or
advisable in furtherance thereof.

        2.07   FISCAL YEAR

        The fiscal year of the Company shall be the calendar year ("Corporate
Year").

        2.08   DELAWARE AGENT FOR SERVICE OF PROCESS

        The name of the initial agent for service of process on the Company in
Delaware is Corporation Trust Company, 1209 Orange Street, Wilmington, DE 19801.

        2.09   ACCOUNTANTS TO THE COMPANY

        An independent certified public accounting firm mutually selected by
Suntory and ICOS shall act as independent accountants to the Company pursuant to
an engagement letter substantially in form attached hereto as Exhibit E.

        2.10   INITIAL CAPITAL

        The initial capital of the Company shall consist of a total of six
thousand (6,000) shares of Common Stock.

        2.11   SUBSCRIPTION

        Suntory hereby subscribes for three thousand (3,000) shares of Common
Stock of the Company, and ICOS hereby subscribes for three thousand shares
(3,000) shares

          *   Confidential Treatment Requested

                                       4
<PAGE>

of Common Stock of the Company.  The subscription price for all
shares shall be TEN THOUSAND DOLLARS (US$10,000) per share and shall be payable
as follows:

    2.11.1 Suntory shall pay its full subscription price by cashier's or
certified check or by wire transfer from Suntory to the Company's account at a
bank to be designated by both Suntory and ICOS ("Corporate Bank Account") on the
Closing Date of the full subscription price of THIRTY MILLION DOLLARS
(US$30,000,000).

    2.11.2 ICOS shall pay its full subscription price by execution and delivery
on the Closing Date of the [   *   ].  The Parties acknowledge and agree that
the fair market value of such contribution shall be THIRTY MILLION DOLLARS
(US$30,000,000).

    2.12   ADDITIONAL CAPITAL

    2.12.1 Subject to Paragraph 2.14 below, no additional capital stock may be
issued by the Company other than by the mutual written consent of Suntory and
ICOS.  The Parties hereto shall meet no less frequently than annually following
the formation of the Company to determine its capital needs and the business and
Development Program for the next succeeding year.

    2.12.2 Upon expenditure of substantially all of the initial capital
contribution to Company pursuant to Paragraph 2.11 above (together with interest
earned by the Company on the cash so contributed), Suntory and ICOS shall each
contribute [   *   ] as additional capital to the Company.

    2.12.3 In the event that the capital contributions to the Company pursuant
to Paragraphs 2.11 and 2.12.2 above (together with interest earned by the
Company on the cash so contributed) are insufficient to fund the activities of
the Company and the Development Program until such time as [   *   ].  Upon
written notification by the Company's Board of Directors to Suntory and ICOS
that the Company [   *   ] of the PAF-AH Technology and to accomplish the
business purposes of the Company as contemplated by this Agreement, Suntory and
ICOS shall promptly meet with management of the Company to [   *   ] by the
Company under the circumstances.  Suntory and ICOS shall thereafter enter into a
mutually acceptable agreement with respect to such additional capital
contributions, if any.

          *   Confidential Treatment Requested

                                       5
<PAGE>

        2.13            WITHDRAWALS

          Except as otherwise specifically provided in this Agreement, neither
Suntory nor ICOS shall have the right to withdraw or to demand a return of all
or any part of its capital contribution.

        2.14            DEFAULT ON ADDITIONAL CAPITAL CONTRIBUTION OBLIGATION

To the extent that either Suntory or ICOS fails to contribute its proportionate
share of the additional capital called for under Paragraph 2.12 above, then from
and after the date such capital was to have been contributed to the Company, the
shareholding percentages of Suntory or ICOS shall promptly be adjusted by the
Company to reflect the increase in capital contributed by either Suntory or ICOS
such that the shareholding interest of Suntory and ICOS shall accurately reflect
the percentage of each Party's total capital contribution as it bears to the
aggregate capital contributions of both Suntory and ICOS.

        2.15            TITLE TO PROPERTY

           Legal title to any and all property of the Company shall be taken and
at all times held in the name of the Company.

3.         CLOSING

          The Closing hereunder shall take place at the offices of ICOS, 22021
20th Avenue S.E., Bothell, Washington, U.S.A., at 10:00 a.m. Pacific Standard
Time on February 6, 1997 ("Closing" and the "Closing Date"), or such other date
and/or place as shall be mutually agreed to by Suntory and ICOS.

4.         CLOSING DOCUMENTS

          At the Closing, each Party shall deliver such documents, instruments
and materials as are called for by this Agreement or as may be reasonably
required in order to carry out the provisions and purposes hereof, all of which
shall be satisfactory in substance and form to legal counsel for each Party.
Without limitation as to the foregoing and in addition to the various documents,
instruments and agreements contemplated in Paragraphs 7 and 8 below, the Parties
agree that, upon the request of any Party, each of them will from time to time
after the Closing Date execute, acknowledge and deliver or cause to be so done,
at their expense, any and all such further documents and instruments as may be
reasonably required for carrying out the purposes of this Agreement.
Simultaneously with such delivery and the Closing, all steps shall be taken as
may be reasonably required to put the Company in

                                       6
<PAGE>

actual possession and operating control of the Background Technology in the
Field of Activity.

5.         REPRESENTATIONS AND WARRANTIES OF ICOS

          To induce Suntory to enter into this Agreement, ICOS represents and
warrants to Suntory as of the date hereof as follows:

        5.01            GOOD STANDING

          ICOS is a corporation duly organized, validly existing and in good
standing under the laws of the State of Delaware and has all requisite power and
authority to:  (i) own its assets to be conveyed in connection with this
Agreement; (ii) lawfully carry on its business as now being conducted; and (iii)
to make, execute, deliver and perform this Agreement and all contracts and
documents to be executed in connection herewith.

        5.02            AUTHORIZATION

          This Agreement has been duly authorized and, prior to the Closing
Date, will be approved by all necessary corporate action of ICOS and will be a
valid and legally binding obligation of ICOS in accordance with its terms.

        5.03            NO BREACH

          Neither execution or delivery of this Agreement, the contracts and
instruments to be executed in connection herewith, nor its performance by ICOS
will conflict with, violate or result in a breach of any term, condition or
provision of, nor constitute a material default under, or result in the
acceleration of any material obligation under, or permit the termination of any
indenture, material contract or other material agreement to which ICOS is a
party or by which ICOS or its properties is subject or bound; nor will such
execution, delivery or performance by ICOS conflict with or violate the
provisions of any judgment, decree, order to which ICOS is subject or ICOS's
restated Articles of Incorporation or Bylaws, or to the best of its knowledge,
any law or regulation.

        5.04            TITLE

          ICOS has valid legal title or rights in and to all of the assets to be
licensed to the Company on the Closing Date pursuant to the PAF-AH License
Agreement, including, but not limited to, Background Technology, free and clear
of all security interests, liens, charges and encumbrances whatsoever and to the
best of ICOS's knowledge, tax or other inchoate liens.  ICOS owns and has the
right to use the

                                       7
<PAGE>

Background Technology in existence as of the date hereof and to be in existence
as of the Closing Date. To the best of ICOS's knowledge: (i) the Background
Technology in existence as of the date hereof and to be in existence as of the
Closing Date do not conflict with the rights of others; (ii) there are no
infringements by third parties of any letters patent or patent applications
which are part of the Background Technology in existence as of the date hereof
and to be in existence as of the Closing Date; and (iii) ICOS's operations and
business as conducted as of and prior to the Closing Date with respect to patent
applications which are part of the Background Technology in existence as of the
date hereof and to be in existence as of the Closing Date do not infringe upon
the rights of any person and/or entity not a Party hereto. No right, privilege,
permission or license, express or implied, under the Background Technology in
existence as of the date hereof and to be in existence as of the Closing Date,
has been granted or is in force pursuant to which any party, other than the
Company, Suntory or ICOS, may make, have made, use or sell any Background
Technology in existence as of the date hereof and to be in existence as of the
Closing Date. No claims have been asserted by any person relating to the
Background Technology in existence as of the date hereof and to be in existence
as of the Closing Date or challenging or questioning the validity or
effectiveness of any license or agreement related thereto, and there is no valid
basis for any such claim. As of the date hereof, Schedule A attached to the form
of PAF-AH License Agreement attached hereto as Exhibit A contains a true,
accurate and complete listing of all patents and patent applications included in
the Background Technology.

        5.05            NO VIOLATIONS

          ICOS is not in violation of any applicable ordinance or statute, or,
to the best of its knowledge, any law or regulation, with respect to its
ownership and operation of the Background Technology in existence as of the date
hereof and to be in existence as of the Closing Date, nor has it received any
notices or citations from any public or quasi-public authority in respect
thereto, including, but not limited to, the Food and Drug Administration.

        5.06            NO LITIGATION

          ICOS is not a party to any pending or threatened suit, action or
legal, administrative, arbitration or other proceeding which might materially
and adversely affect the business of the Company, the Background Technology in
existence as of the date hereof or to be in existence as of the Closing Date, or
the transactions contemplated by this Agreement, nor does ICOS know of any facts
which are likely with the passage of time to give rise to such a suit, action or
proceeding.

                                       8
<PAGE>

        5.07            REPRESENTATIONS AND WARRANTIES

          No representation or warranty of ICOS, nor any exhibit, document,
statement, certificate or schedule furnished to Suntory pursuant hereto or in
connection with the transactions contemplated hereby, contains any untrue
statement of a material fact, or omits to state a material fact necessary to
make statements or facts contained therein not misleading.  The representations
and warranties of ICOS set forth in this Agreement and in any exhibit, document,
statement, certificate or schedule furnished or to be furnished pursuant hereto
shall be true on and as of the Closing Date as though such representations and
warranties were made on and as of the Closing Date.

6.         REPRESENTATIONS AND WARRANTIES OF SUNTORY

          To induce ICOS to enter into and perform this Agreement, Suntory
represents and warrants to ICOS as of the date hereof as follows:

        6.01            GOOD STANDING

          Suntory is a corporation duly organized and validly existing and in
good standing under the laws of the country of Japan and has all requisite power
and authority to lawfully carry on its business as now being conducted and to
make, execute, deliver and perform this Agreement and all instruments and
documents to be executed in connection herewith.

        6.02            AUTHORIZATION

          This Agreement has been duly authorized and, prior to the Closing
Date, will be approved by all necessary corporate action of Suntory and will be
a valid and legally binding obligation of Suntory in accordance with its terms.

        6.03            NO BREACH

          Neither execution or delivery of this Agreement, the contracts and
instruments to be executed in connection herewith, nor its performance by
Suntory will conflict with, violate or result in a breach of any term, condition
or provision of, nor constitute a material default under, or result in the
acceleration of any material obligation under, or permit the termination of any
indenture, material contract or other material agreement to which Suntory is a
party or by which Suntory or its properties is subject or bound; nor will such
execution, delivery or performance by Suntory conflict with or violate the
provisions of any judgment, decree, order to which Suntory is subject or
Suntory's Bylaws, or to the best of its knowledge, any law or regulation.

                                      9
<PAGE>

        6.04            NO LITIGATION

          Suntory is not a party to any pending or threatened suit, action or
legal, administrative, arbitration or other proceeding which might materially
and adversely affect the transactions contemplated by this Agreement, nor does
Suntory know of any facts which are likely with the passage of time to give rise
to such a suit, action or proceeding.

        6.05            REPRESENTATIONS AND WARRANTIES

          No representation or warranty of Suntory, nor any exhibit, document,
statement, certificate or schedule furnished or to be furnished to ICOS pursuant
hereto or in connection with the transactions contemplated hereby, contains or
will contain any untrue statement of a material fact, or omits or will omit to
state a material fact necessary to make statements or facts contained therein
not misleading.  The representations and warranties of Suntory set forth in this
Agreement and in any exhibit, document, statement, certificate or schedule
furnished or to be furnished pursuant hereto shall be true on and as of the
Closing Date as though such representations and warranties were made on and as
of Closing Date.

7.         CONDITIONS PRECEDENT TO THE OBLIGATIONS OF SUNTORY

          All of the obligations of Suntory under this Agreement are subject to
the fulfillment, at or prior to the Closing Date, of each of the following
conditions:

        7.01            NO MISREPRESENTATIONS

          Suntory shall not have discovered any material error, misstatement or
omission in the representations and warranties made by ICOS in Paragraph 5
above.

        7.02            COMPLIANCE WITH AGREEMENT

          ICOS shall have performed and complied with all agreements, covenants
and conditions required by this Agreement prior to the Closing Date.

        7.03            DELIVERY

           Suntory shall have had delivered to it each of the following:

            7.03.1 Confirmation in form and substance reasonably satisfactory to
Suntory evidencing receipt of ICOS's capital contribution specified in Paragraph
2.11 above;

                                      10
<PAGE>

            7.03.2 Duly executed counterpart of the PAF-AH License Agreement
effective to [ * ] together with such other documents and instruments as may be
necessary to effectuate the licensing contemplated by this Agreement;

            7.03.3 Duly executed counterparts of the Bylaws and Organizational
Minutes of the Company;

            7.03.4 Duly executed, validly authorized and issued, fully paid and
nonassessable Common Stock represented by Certificate No. 1, duly issuing three
thousand (3,000) shares thereof to Suntory;

            7.03.5 Duly executed counterpart of the Development and Supply
Agreement;

            7.03.6 Duly executed counterparts of the Suntory and ICOS Services
Agreements, which are attached hereto as Exhibits F and G, respectively
("Services Agreements");

            7.03.7 Duly executed counterparts of the Suntory and ICOS License
Agreements, which are attached hereto as Exhibits H and I, respectively
("License Agreements");

            7.03.8 Opinion of ICOS's counsel (as defined in Paragraph 7.04
below);

            7.03.9 Duly executed counterpart of the Right of First Negotiation
Agreement, which is attached hereto as Exhibit J; and

            7.03.10  Duly executed certificate from an officer of ICOS that the
representations and warranties of ICOS contained in Paragraph 5 are true and
correct as of the Closing Date.

        7.04            OPINION OF COUNSEL

          ICOS shall have delivered to Suntory an opinion of Perkins Coie, legal
counsel for ICOS, in a form satisfactory to counsel for Suntory, dated as of the
Closing Date, to the effect that (i) ICOS is a corporation duly organized,
validly existing and in good standing under the laws of the State of Delaware,
and ICOS has the corporate power to conduct its business where such business is
now conducted and to execute and


          *   Confidential Treatment Requested

                                      11
<PAGE>

deliver this Agreement; (ii) the execution, delivery and performance of this
Agreement, together with all instruments and documents executed in connection
therewith, and the transactions contemplated hereby have been duly authorized
and approved by the Board of Directors of ICOS; (iii) this Agreement, together
with all instruments and documents executed in connection herewith, constitutes
valid and binding obligations of ICOS, enforceable in accordance with their
terms, except as limited by bankruptcy, insolvency or other laws of general
application relating to or affecting the enforcement of creditors' rights; and
(iv) the execution, delivery and performance by ICOS, together with all
instruments and documents executed in connection therewith, and the consummation
of the transactions contemplated hereby will not result in any conflict with, or
material breach or violation by ICOS of, or default by ICOS under, its Articles
of Incorporation, Bylaws, or any judgment, decree, order, or indenture, material
obligation or agreement, or other material instrument or document of, or
applicable to, them known to such legal counsel.

          In rendering the foregoing opinion, Perkins Coie may rely on opinions
of other counsel, reasonably acceptable to Suntory, and, as to matters of fact,
on searches of public records and certificates of officers and directors of
ICOS.

        7.05            NO LITIGATION

          No suit, action or proceeding against ICOS shall be pending or
threatened before any court or governmental agency in which it is sought to
restrain or prohibit or to obtain damages or other relief in connection with
this Agreement or the transactions contemplated hereby.

        7.06            ADDITIONAL DOCUMENTS

          ICOS shall have delivered to Suntory such other instruments and
documents as may be, in the opinion of counsel for Suntory, reasonably necessary
to effectuate the transactions contemplated by this Agreement, and all legal
matters in connection with this Agreement and the transactions contemplated
hereby shall have been approved by counsel for Suntory.

        7.07            HART-SCOTT-RODINO CLEARANCE

          The waiting period described in Section 7A of the Clayton Act, 15
U.S.C. (S) 18a has expired without adverse action by the Federal Trade
Commission ("FTC") or Department of Justice ("DJ") of the United States, or an
affirmative response has been received from the FTC or DJ which has the effect
of shortening the waiting period.

                                      12
<PAGE>

8.        CONDITIONS PRECEDENT TO THE OBLIGATIONS OF ICOS

          All of the obligations of ICOS under this Agreement are subject to the
fulfillment, at or prior to the Closing Date, of each of the following
conditions:

    8.01  NO MISREPRESENTATIONS

          ICOS shall not have discovered any material error, misstatement or
omission in the representations and warranties made by Suntory in Paragraph 6
above.

    8.02  COMPLIANCE WITH AGREEMENT

          Suntory shall have performed and complied with all agreements,
covenants and conditions required by this Agreement prior to the Closing Date.

    8.03  DELIVERY

          ICOS shall have had delivered to it each of the following:

    8.03.1 Confirmation in form and substance reasonably satisfactory to ICOS
evidencing receipt of Suntory's monetary capital contribution in the amount
specified in Paragraph 2.11 above;

    8.03.2 Duly executed counterparts of the Bylaws and Organizational Minutes
of the Company;

    8.03.3 Duly executed, validly authorized and issued, fully paid and
nonassessable Common Stock represented by Certificate No. 2, duly issuing three
thousand (3,000) shares thereof to ICOS;

    8.03.4 Duly executed counterpart of the Development and Supply Agreement;

    8.03.5 Duly executed counterparts of the Services Agreements;

    8.03.6 Duly executed counterparts of the License Agreements;

    8.03.7 Opinion of Counsel to Suntory (as defined in Paragraph 8.04 below);
and

    8.03.8 Duly executed certificate from an officer of Suntory that the
representations and warranties of Suntory contained in Paragraph 6 are true and
correct as of the Closing Date.

                                      13
<PAGE>

        8.04  OPINION OF COUNSEL

        Suntory shall have delivered to ICOS an opinion of Cleary, Gottlieb,
Steen & Hamilton, legal counsel for Suntory, in a form satisfactory to counsel
for ICOS, dated as of the Closing Date, to the effect that (i) Suntory is a
corporation duly organized, validly existing and in good standing under the laws
of Japan and Suntory has the corporate power to conduct its business where such
business is now conducted and to execute and deliver this Agreement; (ii) the
execution, delivery and performance of this Agreement, together with all
instruments and documents executed in connection herewith, and the transactions
contemplated hereby have been duly authorized and approved by the Board of
Directors of Suntory; (iii) this Agreement, together with all instruments and
documents executed in connection therewith, constitutes valid and binding
obligations of Suntory, enforceable in accordance with their terms, except as
limited by bankruptcy, insolvency or other laws of general application relating
to or affecting the enforcement of creditors' rights; and (iv) the execution,
delivery and performance by Suntory, together with all instruments and documents
executed in connection therewith, and the consummation of the transactions
contemplated hereby will not result in any conflict with, or material breach or
violation by Suntory of, or default by Suntory under, its Articles of
Incorporation, Bylaws, or any judgment, decree, order, or indenture, material
obligation or agreement, or other material instrument or document of, or
applicable to, them known to such legal counsel.

        In rendering the foregoing opinion, Cleary, Gottlieb, Steen & Hamilton
may rely on opinions of other counsel, reasonably acceptable to ICOS, and, as to
matters of fact, on searches of public records and certificates of officers and
directors of Suntory.

        8.05  NO LITIGATION

        No suit, action or proceeding against Suntory shall be pending or
threatened before any court or governmental agency in which it is sought to
restrain or prohibit, or to obtain damages or other relief in connection with,
this Agreement or the transactions contemplated hereby.

        8.06  ADDITIONAL DOCUMENTS

        Suntory shall have delivered to ICOS such other instruments and
documents as may be, in the opinion of counsel for ICOS, reasonably necessary to
effectuate the transactions contemplated by this Agreement, and all legal
matters in connection with this Agreement and the transactions contemplated
hereby shall have been approved by counsel for ICOS.

                                      14
<PAGE>

9.         SURVIVAL AND INDEMNIFICATION

        9.01    SURVIVAL OF REPRESENTATIONS AND WARRANTIES

        The respective representations and warranties of Suntory and of ICOS
shall survive the Closing and continue in full force and effect for a period
thereafter equal to [   *   ] following the Closing Date.

        9.02    INDEMNIFICATION

        ICOS shall indemnify and hold Suntory, the Company and their
respective directors, officers, employees and agents harmless from and against
any and all claims, liabilities, losses, costs, damages and expenses, including
costs of investigation, court costs and reasonable attorneys' fees, to which any
of them may become subject arising from or in any manner connected with,
directly or indirectly, any material misstatement, error or omission in any
representation or warranty of ICOS contained in this Agreement (without effect
upon ICOS's liability under the various instruments and documents to be executed
in connection herewith).  Suntory agrees to indemnify ICOS, the Company and
their respective directors, officers, employees and agents, to the same extent
that Suntory is being indemnified pursuant to the immediately preceding
sentence.

        9.03    MECHANISM

        The Party seeking indemnification hereunder ("Indemnified Party")
shall give written notice to the indemnifying Party or Parties ("Indemnifying
Party") of its indemnification claims hereunder, specifying the amount and
nature of the claim, and giving the Indemnifying Party the right to contest any
such claim represented by counsel of its choice; if any such claim is made
hereunder by the Indemnified Party and such claim arises from the claims of a
third party against the Indemnified Party and the Indemnifying Party does not
elect to undertake the defense thereof by written notice within fifteen (15)
days after receipt of the original notice from the Indemnified Party, the
Indemnified Party shall be entitled to indemnity pursuant to the terms of this
Agreement to the extent of its payment in respect of such claim.  To the extent
that the Indemnifying Party undertakes the defense of such claim in good faith
by proceeding diligently at its expense, and without materially impairing the
financial conditions or operations of the Indemnified Party, the Indemnified
Party shall be entitled to indemnity hereunder only if, and to the extent that,
such defense is


        *Confidential Treatment Requested

                                     -15-
<PAGE>

unsuccessful as determined by a final judgment of a court of competent
jurisdiction or is settled with the consent of the Indemnifying Party. The Party
defending a third-party claim shall have the right to choose its own counsel.

10.       BROKERS

          Each of the Parties represents and warrants that it has dealt with no
broker or finder in connection with any of the transactions contemplated by this
Agreement, and, insofar as it knows, no broker or other person is entitled to
any commission or finder's fee in connection with any of these transactions.
The Parties hereto each agree to indemnify and hold harmless one another against
any loss, liability, damage, cost, claim or expense, including reasonable
attorneys' fees, incurred by reason of any brokerage, commission or finder's fee
alleged to be payable because of any act, omission or statement of the
Indemnifying Party.

11.     MANAGEMENT

        11.01   BOARD OF DIRECTORS

        The Company shall be managed by a Board of Directors consisting
initially of six (6) members.  Suntory and ICOS shall each have the right to
nominate three (3) members of the Board of Directors.  In the event of a default
in the payment of any additional capital contribution, as described in Paragraph
2.14 above, until such default is cured, the authorized number of members of the
Board of Directors shall be increased to seven (7) and four (4) of such members
shall be nominees of the nondefaulting Party.  The number of members of the
Board of Directors cannot be decreased or otherwise increased without the mutual
written consent of Suntory and ICOS.  All actions by the Board of Directors
shall require the affirmative vote of four (4) or more  members of the Board of
Directors at a meeting at which a quorum is present, except for such actions as
to which a higher than majority vote is required pursuant to the provisions of
this Agreement, the Articles, the Bylaws or applicable law.

        11.02   OFFICERS

        The Company shall have a Chairman of the Board, Chief Executive
Officer/President, Vice President - ICOS, Vice President - Suntory,
Secretary/Assistant Chief Financial Officer, Chief Financial Officer/Assistant

                                     -16-
<PAGE>

Secretary and such other officers with such titles and duties as the Board of
Directors may determine.  Any two or more offices may be held by the same
person. [   *   ].

        11.03    ACTIONS REQUIRING CONSENT

        In addition to any other items referred to in this Agreement requiring
consent of both of Suntory and ICOS, none of the following actions shall be
permitted to be taken by the Company unless it shall have obtained the consent
of both Suntory and ICOS:

           (i)   [   *   ] the Field of Activity;

           (ii)  Any [   *   ] by the Company;

           (iii) The [ * ] of the Company having a fair market value in excess
                 of [ * ] by the Company (other than in connection with the
                 sale of products and services in the ordinary course of its
                 business) or [ * ] (regardless of value) in the [ * ];

           (iv)  The adoption of a business plan, annual capital, operating and
                 development plans and budgets, including any material
                 modification thereof ("Business Documents");

           (v)   Any capital expenditure in excess of [   *   ] by the Company;
                 and

           (vi)  Any material act in material contravention of this Agreement.

        11.04     ACCOUNTING AND INTERNAL CONTROLS

          Suntory and ICOS shall cause the management of the Company to conduct
the business of the Company at all times in accordance with high standards of
business ethics and to maintain the Company's accounts in accordance with
generally accepted accounting principles consistently applied and, specifically,
to:

           (i) Maintain full and accurate books, records, and accounts which
               shall, in reasonable detail, accurately and fairly reflect all
               transactions of the Company; and

          *Confidential Treatment Requested

                                     -17-
<PAGE>

           (ii)   Devise and maintain a system of internal accounting controls
                  sufficient to provide reasonable assurances that (a)
                  transactions are executed in accordance with general or
                  specific authorizations, and (b) transactions are recorded as
                  necessary to permit preparation of financial statements in
                  conformity with generally accepted accounting principles, to
                  permit preparation of all tax returns and to maintain
                  accountability for assets.

        11.05  FINANCIAL AND BUSINESS INFORMATION AND TAX RETURNS

           Suntory and ICOS shall cause the management of the Company to:

           (i)    Present Business Documents to the Board of Directors and
                  Suntory and ICOS for approval;

           (ii)   Make available to all members of the Board of Directors
                  together with Suntory and ICOS on a regular basis, and as
                  reasonably requested, all such information and/or documents as
                  may be required to permit the Board of Directors and/or
                  Suntory and ICOS, as the case may be, to make informed
                  judgments with respect to such Business Documents and all
                  other matters of interest to them;

           (iii)  Prior to March 15 of each Corporate Year, provide to Suntory
                  and ICOS regular annual audited financial statements by the
                  Company's independent certified public accountants, which
                  shall include a statement of profits and losses, changes in
                  financial position and a balance sheet for the year then
                  ended, as well as such other appropriate financial information
                  reasonably requested by the Parties; and

           (iv)   Cause to be prepared all federal, state and local tax returns
                  of the Company ("Returns").

        11.06  BANK ACCOUNTS

          All funds of the Company shall be deposited in the name of the Company
in such bank account or accounts as shall be determined by mutual agreement of
Suntory and ICOS.  All withdrawals therefrom shall be made upon checks signed on
behalf of

                                     -18-
<PAGE>

the Company by any one officer, except for (i) amounts in excess of [ * ] and
(ii) any payments to be made to Suntory and/or ICOS or their respective
affiliates, in which case all such checks shall require the signature of one (1)
Suntory officer and one (1) ICOS officer. The Parties hereto shall not make
deposits in or issue any checks against the Company bank account(s) without
full, proper and complete supporting records.

        11.07   INDEPENDENT ENTERPRISE

          Suntory and ICOS agree to cause the Company at all times to be
conducted as an independent enterprise for profit.  Except as otherwise provided
herein, all commercial transactions between the Company and Suntory and/or ICOS
(or their affiliates) shall be conducted on an arm's-length basis with neither
granting to the other terms or conditions more favorable than would be accorded
unrelated third parties, except as Suntory and ICOS may otherwise mutually agree
prior to such transactions.

        11.08   COMPENSATION OF OFFICERS AND DIRECTORS

          The officers and members of the Board of Directors of the Company will
serve in their respective positions for no compensation or remuneration
whatsoever.

        11.09   FIDUCIARY DUTY

          Suntory, ICOS, the officers and members of the Board of Directors of
the Company shall all have the fiduciary responsibility for the safekeeping and
use of all funds and assets (including records) of the Company, whether or not
in immediate possession or control, for the exclusive benefit of the Company and
its shareholders.

        11.10   OTHER ACTIVITIES

          Suntory and ICOS may engage in or possess an interest in other
business ventures of any nature or description, independently or with others,
whether presently existing or hereafter created, other than for the purpose of
development, manufacture, production and sale of PAF-AH Products.


          *Confidential Treatment Requested

                                     -19-
<PAGE>

        11.11           NONCOMPETITION

          Except as specifically authorized by their respective License
Agreements, Suntory and ICOS shall not, directly or indirectly, nor shall they
permit any of their respective subsidiaries, as applicable, to engage in any
business that makes or sells products that are substantially the same as the
business of the Company in the Field of Activity for a period of [   *   ]
from and after the Closing Date anywhere in the world, it being recognized that
the business of the Company is worldwide.

12.        BUSINESS MATTERS

        12.01   LICENSE AGREEMENTS

           As more fully set forth in those certain License Agreements, Suntory
and ICOS agree that:

           (i)    Suntory will have an [   *   ].

           (ii)   ICOS will have an [   *   ].

           (iii)  The Parties recognize that the Company may [   *   ].

        12.02   DEVELOPMENT PROGRAM

          As more fully set forth in the Development and Supply Agreement,
Suntory and ICOS agree to conduct on behalf of the Company, on an accelerated
and coordinated basis, [   *   ] necessary for the Company to engage in the
Field of Activity and manufacture and sell PAF-AH Products in the Company
Territory.

        12.03   SERVICES AGREEMENTS

          As more fully set forth in those certain Services Agreements, Suntory
and ICOS agree that each will provide certain services to the Company in order
to promote the business of the Company in the Field of Activity.


          *Confidential Treatment Requested

                                     -20-
<PAGE>

13.     RESTRICTIONS ON SHARES

        13.01   OVERALL RESTRICTIONS

The Company will be owned on the Closing Date by two (2) entities which have the
compatibility and financial stability which are major elements contributing
toward the prospect of the future success of the Company.  Except in accordance
with the terms of this Agreement, neither Suntory nor ICOS shall sell, transfer,
assign, pledge, hypothecate or in any other way dispose of or encumber,
voluntarily or involuntarily, by bankruptcy, operation of law or otherwise (any
such event is referred to as a "Transfer") any of its shares or any right or
interest therein without the prior written consent of the other
("Nontransferring Shareholder").  Unless such prior written consent is given,
the proposed Transfer may not take place, and any attempted Transfer in
derogation hereof shall be deemed null and void.  If for any reason any clause
or provision of this Paragraph 13.01 should be held unenforceable, invalid or in
violation of law by any court or tribunal, then the Nontransferring Shareholder
shall have the right, exercisable in writing within ninety (90) days of the date
of final determination of invalidity or unenforceability, to purchase all of the
shares which such transferring shareholder purported to Transfer, pursuant to
the terms of Paragraph 13.03 below.

        13.02   ADDITIONAL RESTRICTIONS

          Upon the occurrence of any of the following events with respect to
Suntory or ICOS ("Occurrence Shareholder") (wherein there is not a continuity of
proprietary interest of the shareholders of Suntory or ICOS who owned shares of
Suntory or ICOS, as the case may be, prior to the occurrence of such an event):
[   *   ].  The Occurrence Shareholder shall notify the other Party in writing
of any occurrence described above in this Paragraph 13.02 at the very earliest
time practicable.

        13.03   PURCHASE PRICE AND PAYMENT DATE

          For purposes of Paragraphs 13.01 and 13.02 above, the purchase price
to be paid for each share of the transferring shareholder or Occurrence
Shareholder shall be computed as follows:

           (i)    Within [   *   ] after the occurrence of an event described in
                  Paragraph 13.01 or 13.02 above, Suntory and ICOS either (a)
                  shall jointly appoint an investment banking firm or (b)
                  failing


          *Confidential Treatment Requested

                                     -21-
<PAGE>

                  this joint action, each separately shall designate an
                  investment banking firm and within [   *   ] after their
                  appointment, the designated investment banking firms shall
                  designate an additional investment banking firm ("Neutral
                  Investment Banker") (collectively, the Neutral Investment
                  Banker and the two investment banking firms designated by the
                  Parties being referred to as the "Three Investment Bankers").
                  The failure by either Suntory or ICOS to appoint an investment
                  banking firm within the time allowed shall be deemed
                  equivalent to appointing the other Party's investment banking
                  firm as the jointly appointed investment banking firm. Within
                  [   *   ] after the appointment of the jointly appointed
                  investment banking firm or the Neutral Investment Banker, as
                  the case may be, the jointly appointed investment banking firm
                  or the Three Investment Bankers, by a majority vote, shall
                  render their appraisal of the fair market value of shares
                  being purchased, [   *   ]. The Company shall bear all
                  appraisal expenses.

           (ii)   The payment date of the purchase price pursuant to this
                  Paragraph 13.03 shall not be later than [   *   ] after the
                  [   *   ] period set forth in Paragraph 13.02 above.

        13.04  CHANGE OF CONTROL

          In the event of a Change in Control (as hereafter defined) of Suntory
or ICOS (the "Acquired Shareholder"), the other Party (the "Other Shareholder")
shall be [   *   ].

          For purposes of this Paragraph 13.04, a "Change in Control" occurs
when any person becomes, after the date hereof, the beneficial owner, directly
or indirectly, of more than fifty percent (50%) of the  outstanding securities
of the Acquired Shareholder (or its holding company) having a right to vote in
the election of directors, except a "Change in Control" will not have occurred
if, after the transaction, fifty percent (50%) or more of the outstanding voting
securities of the corporation acquiring the Acquired Shareholder's voting
securities are owned by the Acquired Shareholder's shareholders in the same
proportion as they own the Acquired Shareholder's voting securities immediately
prior to such transaction.  It is recognized and agreed that a holding company
currently holds a substantial portion (more than



          *Confidential Treatment Requested

                                     -22-
<PAGE>

fifty percent (50%)) of Suntory's outstanding securities having a right to vote
in the election of directors, that such holding company is owned and controlled
by family members and that the transfer, after the date hereof, of the voting
securities of the holding company among the family members will not constitute a
"Change in Control" of Suntory.

        13.05   DELIVERY OF SHARES; TERMINATION OF AGREEMENTS

          Any purchase of shares pursuant to this Agreement shall take place on
the payment date thereof.  The certificates representing all of the shares so
purchased shall be duly endorsed and delivered to the purchaser(s) thereof on
the payment date.  As of the payment date, this Agreement, the Development and
Supply Agreement and the License Agreement and Services Agreement of the Party
whose shares are purchased shall be terminated.

14.        ADDITIONAL SHARES

          In the event Suntory and/or ICOS acquire any additional shares of the
Company, then any and all such shares shall be subject to the terms and
provisions of this Agreement.

15.        ENDORSEMENT OF CERTIFICATES

           Upon the execution of this Agreement, the certificates of stock
subject hereto shall be endorsed to read as follows:

     "Any sale, assignment, transfer, pledge, bequest or other disposition of
     the shares of stock represented by this Certificate is restricted by and
     subject to the terms and provisions of a Shareholders' Agreement dated
     ____________, 1996 by and among the Company, Suntory and ICOS, a copy of
     which Agreement is on file in the principal office of the Company, which
     Agreement may from time to time hereafter be amended.  The shares of stock
     evidenced by this Certificate have not been registered with the Securities
     and Exchange Commission, but have been issued pursuant to the private
     offering exemption under the Securities Act of 1933, as amended."

           All certificates of stock hereafter issued to or transferred to
Suntory and ICOS shall bear the same endorsement.

                                     -23-
<PAGE>

16.        REDEMPTION OF SHARES

        16.01   EVENTS OF WITHDRAWAL

Suntory or ICOS (the "Withdrawing Party") may, upon sixty (60) days' prior
written notice to the Parties, elect to withdraw from the business efforts of
the Company and have all of its shares of the Company redeemed by the Company
upon the occurrence of any of the following events or situations: [   *   ];
provided, however, that in the event both Suntory and ICOS give notice under
this Paragraph 16.01 within sixty (60) days of each other, the provisions of
this Paragraph 16 shall not apply and the parties will be deemed to have
mutually agreed to dissolve the Company pursuant to Section 20.01(i).

        16.02   REDEMPTION PRICE AND DATE

          For purposes of Paragraph 16.01, the redemption price shall be the
lesser of [   *   ].  Sixty (60) days after the notice of election to withdraw
(or such earlier date as mutually agreed upon), the following shall occur:  (i)
the Company shall pay the redemption price to the Withdrawing Party; (ii) the
Withdrawing Party shall tender to the Company its certificates, duly endorsed,
for all of its shares of the Company; and (iii) this Agreement, the Development
and Supply Agreement and the License Agreement and Services Agreement to which
the Withdrawing Party is a party shall be terminated.

17.        COSTS AND EXPENSES

          Suntory and ICOS shall each bear and pay for their respective costs
and expenses regarding the negotiation and preparation of this Agreement and all
documents, instruments and agreements related thereto.  Costs and expenses
incurred by the Company after the Closing Date shall be paid by the Company.

18.        EXPORT CONTROL LAWS

        18.01   EXPORT LAW COMPLIANCE

Each Party acknowledges and agrees that it does not intend to, nor will it,
export from the United States or re-export from any foreign country, or permit a
third party to export or re-export, any technology or technical information
acquired or created under this Agreement or any other related agreements to a
country where such export or re-


          *Confidential Treatment Requested

                                     -24-
<PAGE>

export would be in violation of U.S. Export Administration Regulations. Each
Party further agrees that the export and re-export of commodities pursuant to
this Agreement and any related agreements shall be subject to the licensing
requirements of the U.S. Export Administration Regulations.

        18.02           SPECIFIC AUTHORIZATION

          In the event that a specific authorization of, or a validated license
from, a government other than that of the exporting party is required, Suntory
and ICOS each agree that the Party, including (if applicable) the Company,
within the jurisdiction of such other government shall, upon the request of the
Party proposing to make the export, use its best efforts to obtain, as
expeditiously as applicable, the requisite authorization or license.

19.        DISTRIBUTIONS OF CASH

          Subject to the terms of Paragraph 20 below, and upon the mutual
consent of Suntory and ICOS, distributions of cash shall be made to Suntory and
ICOS in accordance with their respective aggregate capital contributions.

20.        DISSOLUTION/LIQUIDATION

        20.01           EVENTS OF DISSOLUTION

           (i)    The Company shall be dissolved upon the mutual written consent
                  of Suntory and ICOS.

           (ii)   The Company shall be dissolved upon the occurrence of any of
                  the events set forth in Paragraph 13.02 if the Party which is
                  not the Occurrence Shareholder shall not have exercised the
                  purchase option provided in Paragraph 13.02 and shall have
                  requested, within sixty (60) days after such occurrence, that
                  the Company be dissolved.

           (iii)  The Company may be dissolved for federal and Delaware income
                  tax purposes, but preserved in nominal form for Delaware state
                  law purposes, by either Suntory or ICOS upon the bankruptcy,
                  receivership or insolvency of the other Party or the Company,
                  or upon the material breach of this Agreement by the other
                  Party.

                                     -25-
<PAGE>

        20.02           FINAL ACCOUNTING AND TAX RETURNS

          Upon the dissolution of the Company, a complete and accurate
accounting shall be made by the Company's independent certified public
accountants from the date of the last previous accounting to the date of
dissolution and all required tax returns shall be timely filed in connection
therewith.

        20.03           LIQUIDATION

          Upon the dissolution of the Company, Suntory and ICOS shall each
appoint three (3) individuals who shall jointly act as liquidator to wind up the
Company (and, if either Suntory or ICOS fails to appoint any individuals within
sixty (60) days after the written request of the other Party, the individuals
that shall have been appointed by such other Party within such sixty (60) day
period shall act as the liquidator) (the individuals so appointed, collectively
"Liquidator").  The Liquidator shall have full power and authority to take full
account of the Company's assets and liabilities and to wind up and liquidate the
affairs of the Company in an orderly and business-like manner as is consistent
with obtaining the fair value thereof upon dissolution.  The Company shall
engage in no further business thereafter other than as necessary to operate on
an interim basis, collect its receivables, pay its liabilities and liquidate its
assets.  All proceeds from liquidation shall be distributed in the following
order of priority:  (i) first, to the payment of all creditors of the Company
and the expenses of liquidation; (ii) second, to the establishing of a reserve
which the Liquidator deems reasonably necessary for any contingent, known or
unforeseen liabilities or obligations of the Company; and (iii) third, the
balance of the Company's net assets shall be divided between Suntory and ICOS in
approximately equal value at the direction of the jointly appointed investment
banking firm or the Three Investment Bankers, as the case may be, which shall
render an appraisal of the fair market value of such net assets within sixty
(60) days of appointment as set forth Paragraph 13.03(i) above.

        20.04           CANCELLATION OF CERTIFICATES; TERMINATION

          Upon the completion of the distributions in liquidation of the Company
as provided in this Paragraph 20 (i) the Liquidator shall cause the cancellation
of all share certificates and shall take such other actions as may be
appropriate to finally dissolve and liquidate the Company and (ii) this
Agreement shall terminate.

                                     -26-
<PAGE>

21.        MISCELLANEOUS

        21.01           NOTICES

          All notices, requests, demands and other communications required or
permitted to be given under this Agreement shall be in writing and shall be
mailed to the Party to whom notice is to be given, by telex or facsimile, and
confirmed by first class mail, registered or certified, return receipt
requested, postage prepaid, and properly addressed as follows (in which case
such notice shall be deemed to have been duly given on the third (3rd) day
following the date of such sending):

        "Suntory"  Suntory Limited
                   The Garden Court 8-F
                   4-1 Kioi-cho, Chiyoda-ku
                   Tokyo 102, Japan
                   Attn:  President
                   Pharmaceutical Division

        "ICOS"     ICOS Corporation
                   22021 - 20th Avenue S.E.
                   Bothell, WA 98021
                   U.S.A.
                   Attn:  President

  With a copy to:  Perkins Coie
                   1201 Third Avenue, 40th Floor
                   Seattle, WA 98101-3099
                   U.S.A.
                   Attn:  James R. Lisbakken, Esq.

        "Company"  Suncos Corporation
                   c/o Suntory Limited
                   The Garden Court 8-F
                   4-1 Kioi-cho, Chiyoda-ku
                   Tokyo 102, Japan
                   Attn:  President
                   Pharmaceutical Division

With a copy to:   Suncos Corporation
                  c/o ICOS Corporation
                  22021 - 20th Avenue S.E.
                  Bothell, WA 98021

                                     -27-
<PAGE>

                  U.S.A.
                  Attn:  President

Any Party by giving notice to the others in the manner provided above may change
such Party's address for purposes of this Paragraph 21.01.

        21.02           PUBLICITY AND DISCLOSURE

          All notices to third parties and all other publicity concerning the
transactions contemplated by this Agreement shall be jointly planned and
coordinated by and between the Parties hereto.

        21.03           ENTIRE AGREEMENT; AMENDMENT

          This Agreement (together with all Exhibits attached hereto and all
documents and instruments delivered in connection herewith) constitutes the full
and complete agreement and understanding between the Parties hereto and shall
supersede any and all prior written and oral agreements concerning the subject
matter contained herein.  This Agreement may not be modified or amended, nor may
any provision hereof be waived without a written instrument executed by Suntory,
ICOS and the Company.

        21.04           WAIVER

          No failure or delay by any Party to insist upon the strict performance
of any term, condition, covenant or agreement of this Agreement, or to exercise
any right, power or remedy hereunder or thereunder or consequent upon a breach
hereof or thereof shall constitute a waiver of any such term, condition,
covenant, agreement, right, power or remedy or of any such breach or preclude
such Party from exercising any such right, power or remedy at any later time or
times.

        21.05           ENFORCEMENT

          The shares of stock of the Company are unique and cannot be readily
purchased or sold in the open market.  For this reason, among others, the
Parties hereto will be irreparably damaged in the event that this Agreement is
not deemed to be specifically enforceable, and the Parties hereby agree that
this Agreement shall be specifically enforceable.  Such remedy shall be
cumulative and not exclusive and shall be in addition to any other remedy which
the Parties may have.

        21.06           REMEDIES

          No right, power or remedy herein conferred upon or reserved to any
Party is intended to be exclusive of any other right, power or remedy or
remedies, and each

                                     -28-
<PAGE>

and every right, power and remedy of any Party pursuant to this Agreement or now
or hereafter existing at law or in equity or by statute or otherwise shall to
the extent permitted by law be cumulative and concurrent, and shall be in
addition to every other right, power or remedy pursuant to this Agreement, or
now or hereafter existing at law or in equity or by statute or otherwise and the
exercise or beginning of the exercise by any Party of any one or more of such
rights, powers or remedies shall not preclude the simultaneous or later exercise
by any Party of any or all such other rights, powers or remedies.

        21.07           HEADINGS

          Headings in this Agreement are included for convenience of reference
only and shall not constitute a part of this Agreement for any purpose.

        21.08           EFFECTIVENESS

          Any provision of this Agreement which is prohibited or unenforceable
in any jurisdiction shall as to such jurisdiction be ineffective to the extent
of such prohibition or unenforceability without invalidating the remaining
provisions hereof or affecting the validity or enforceability of such provision
in any other jurisdiction.

        21.09           ATTORNEYS' FEES AND COSTS

          In the event of any action at law or in equity among the Parties
hereto to enforce any of the provisions hereof, the unsuccessful Party or
Parties to such litigation shall pay to the successful Party or Parties all
costs and expenses, including actual attorneys' fees, incurred therein by such
successful Party or Parties; and if such successful Party or Parties shall
recover judgment in any such action or proceeding, such costs, expenses and
attorneys' fees may be included in and made a part of such judgment.  The
successful Party shall be the Party who is entitled to recover its costs of
suit, whether or not the suit proceeds to final judgment.  A Party not entitled
to recover its costs shall not recover attorneys' fees.

        21.10           GOVERNING LAW

          This Agreement shall be governed by and construed in accordance with
the internal laws, and not the law of conflicts, of the State of Delaware
applicable to agreements made and to be performed in such state.

        21.11           BINDING EFFECT; ASSIGNMENT

          This Agreement shall be binding upon and inure to the benefit of the
Parties hereto, their successors and permitted assigns.  This Agreement may not
be assigned

                                     -29-
<PAGE>

in whole or in part by any Party, except with the prior written consent of the
other Parties.

        21.12           EXHIBITS

           All Exhibits attached hereto and referred to herein are hereby
incorporated herein as though fully set forth.

        21.13           NUMBER AND GENDER

          Words in the singular shall include the plural, and words in a
particular gender shall include either or both additional genders, when the
context in which such words are used indicates that such is the intent.

        21.14           COUNTERPARTS

          This Agreement may be executed in one or more counterparts by the
Parties hereto.  All counterparts shall be construed together and shall
constitute one agreement.

        21.15           AGREEMENT TO PERFORM NECESSARY ACTS

          Each Party agrees to perform any further acts and execute and deliver
any and all further documents and/or instruments which may be reasonably
necessary to carry out the provisions of this Agreement and to carry out the
business purpose of the Company.

        21.16           VALIDITY

          If for any reason any clause or provision of this Agreement, or the
application of any such clause or provision in a particular context or to a
particular situation, circumstance or person, should be held unenforceable,
invalid or in violation of law by any court or other tribunal, then the
application of such clause or provision in contexts or to situations,
circumstances or persons other than that in or to which it is held
unenforceable, invalid or in violation of law shall not be affected thereby, and
the remaining clauses and provisions hereof shall nevertheless remain in full
force and effect.

        21.17           REPRESENTATIONS

          Each of the Parties hereto acknowledges and agrees (i) that no
representation or promise not expressly contained in this Agreement has been
made by any other Party hereto or by any of its agents, employees,
representatives or attorneys; (ii) that this

                                     -30-
<PAGE>

Agreement is not being entered into on the basis of, or in reliance on, any
promise or representation, expressed or implied, covering the subject matter
hereof, other than those set forth expressly in this Agreement; and (iii) that
each has had the opportunity to be represented by counsel of its own choice in
this matter, including the negotiations which preceded the execution of this
Agreement.

        21.18           FORCE MAJEURE

          Any Party shall be excused for failures and delays in performance of
its respective obligations under this Agreement caused by war, riots or
insurrections, laws and regulations (including, without limitation, imposition
of export restrictions or controls), strikes, floods, fires, explosions or other
catastrophes beyond the control and without the fault of such Party ("Force
Majeure").  This provision shall not, however, release such Party from using its
best efforts to avoid or remove such cause and such Party shall continue
performance hereunder with the utmost dispatch whenever such causes are removed.
Upon claiming any such excuse or delay for non-performance, such Party shall
give prompt written notice thereof to the other Party.

        21.19           EXPANSION OF BUSINESS

          The Parties contemplate that there may be additional opportunities for
mutual development of other products or areas of interest by the Company.  At
any time either ICOS or Suntory may suggest that such other opportunities be
further discussed.

        21.20           SURVIVAL

          In the event this Agreement is terminated earlier than [   *   ]
after the Closing Date, Paragraph 9 shall survive termination until the
expiration of the period specified in Paragraph 9.01.

          IN WITNESS WHEREOF, the undersigned have caused this Agreement to be
executed by their duly authorized representatives in the manner legally binding
upon them.

          *Confidential Treatment Requested

                                     -31-
<PAGE>

                              ICOS CORPORATION

                              By     /s/ George B. Rathmann
                                 --------------------------
                                 Its Chairman of the Board, President
                                     --------------------------------
                                     and Chief Executive Officer
                                     --------------------------------

                              SUNTORY LIMITED


                              By     /s/ Terumi Nakajima
                                 -----------------------
                                 Its Senior Managing Director
                                     ------------------------

                              SUNCOS CORPORATION


                              By     /s/ Terumi Nakajima
                                 -----------------------
                                 Its President and Chief Executive
                                     -----------------------------
                                     Officer
                                     -----------------------------


                              By   /s/ George B. Rathmann
                                 --------------------------
                                 Its Chairman of the Board
                                     ---------------------

                                     -32-
<PAGE>

                                EXHIBIT SCHEDULE

<TABLE>
<CAPTION>

EXHIBIT                  DESCRIPTION                PARAGRAPH
----------   ------------------------------------   ---------
<S>          <C>                                         <C>

   A         PAF-AH License Agreement............     1.04

   B         Development and Supply Agreement....     1.06

   C         Articles of Incorporation...........     2.04

   D         Bylaws of the Company...............     2.05

   E         Accountants Engagement Letter.......     2.09

   F         Suntory Services Agreement..........     7.03.6

   G         ICOS Services Agreement.............     7.03.6

   H         Suntory License Agreement...........     7.03.7

   I         ICOS License Agreement..............     7.03.7

   J         Right of First Negotiation Agreement     7.03.9
</TABLE>

                                     -33-