<PAGE>

                                                                 EXHIBIT 10.13

              CONFIDENTIAL TREATMENT HAS BEEN REQUESTED FOR CERTAIN
               PORTIONS OF THIS DOCUMENT. SUCH PORTIONS HAVE BEEN
            REDACTED AND MARKED WITH ASTERISKS (**). THE NON-REDACTED
                  VERSION OF THIS DOCUMENT HAS BEEN SENT TO THE
                 SECURITIES AND EXCHANGE COMMISSION PURSUANT TO
                   AN APPLICATION FOR CONFIDENTIAL TREATMENT.

                                LICENSE AGREEMENT

                                     Between

                   PHARMACEUTICAL APPLICATIONS ASSOCIATES LLC
                         C. DONALD WILLIAMS, M.D.C.G.P.
                              ROBERT MURDOCK, R.Ph.

                                       and

                      PRAECIS PHARMACEUTICALS INCORPORATED

                           Dated as of: April 15, 1999
<PAGE>

                                TABLE OF CONTENTS

WITNESSETH.................................................................    1

DEFINITIONS................................................................    2

GRANT OF LICENSE...........................................................    7

DEVELOPMENT AND COMMERCIALIZATION..........................................   10

CONSIDERATION..............................................................   12

PATENT PROSECUTION.........................................................   17

THIRD-PARTY INFRINGEMENT...................................................   19

PRODUCT LIABILITY..........................................................   21

REPRESENTATIONS AND WARRANTIES; INDEMNIFICATION............................   21

ASSIGNMENT.................................................................   25

TERM AND TERMINATION.......................................................   26

INFORMATION................................................................   29

PUBLICATIONS...............................................................   32

NOTICES AND OTHER COMMUNICATIONS...........................................   33

DISPUTE RESOLUTION.........................................................   34

MISCELLANEOUS PROVISIONS...................................................   36

EXHIBIT A (U.S. Patent Application No. 3742-901-2-IPROV
and related filings).......................................................  A-1

EXHIBIT B ( List of Individuals and Entities)..............................  B-1



                                        i
<PAGE>

                                LICENSE AGREEMENT

            This Agreement is made and entered into as of the 15th day of April,
1999, (the "Effective Date") by and between Pharmaceutical Applications
Associates LLC, a limited liability company organized and existing under the
laws of the State of [ ] and having its principal office at 402 East Yakima
Avenue, Suite 330, Yakima, Washington 98901-2760 (hereinafter referred to as
"PAA"), C. Donald Williams, M.D.C.G.P. and Robert Murdock, R.Ph., each of whom
is a member of PAA (collectively, the "PAA Principals"), and PRAECIS
PHARMACEUTICALS INCORPORATED, a corporation organized and existing under the
laws of the State of Delaware and having its principal office at One Hampshire
Street, 5th Floor, Cambridge, Massachusetts 02139-1532 (hereinafter referred to
as "Licensee").

                                   WITNESSETH

            WHEREAS, PAA is the sole owner of the Technology (as later defined
herein), and has the right to grant the licenses granted herein with respect to
the Technology;

            WHEREAS, Licensee wishes to acquire certain exclusive license rights
with respect to the Technology for the purpose of developing and commercially
exploiting the Technology, upon the terms and conditions hereinafter set forth;

            WHEREAS, PAA is the sole owner of the Patent Application (as later
defined herein), and has the right to grant the licenses granted herein with
respect to the

<PAGE>

Patent Rights, the Licensed Products and the Licensed Processes (each as later
defined herein), upon the terms and conditions hereinafter set forth; and

            WHEREAS, Licensee desires to obtain a license to the Patent Rights,
the Licensed Products and the Licensed Processes, upon the terms and conditions
hereinafter set forth.

            NOW, THEREFORE, in consideration of the premises and the
representations, warranties and agreements contained herein, and for other good
and valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto agree as follows:

                                 1 - DEFINITIONS

            For the purposes of this Agreement, the following words and phrases
shall have the following meanings:

            1.1 An "Affiliate" of a party shall mean a company or other entity
which controls, is controlled by, or is under common control with such party. A
corporation or other entity shall be regarded as in control of another
corporation or entity if it owns or directly or indirectly controls more than
fifty percent (50%) of the voting stock or other ownership interest of the other
corporation or entity, or if it possesses, directly or indirectly, the power to
direct or cause the direction of the management and policies of the corporation
or other entity or the power to elect or appoint fifty percent (50%) or more of
the members of the governing body of the corporation or other entity.


                                       2
<PAGE>

            1.2 "Developments" shall mean any findings, discoveries, inventions,
additions, modifications, formulations or changes made by or on behalf of either
party during the term of this Agreement which relate to the Technology, any
Licensed Product or any Licensed Process including, without limitation, new or
improved formulations or methods of administration, improvements in clinical
efficacy, improved side effect profiles, new medical indications for any
Licensed Product and improvements in the manufacturing process for any Licensed
Product; provided that Developments shall not include any of the foregoing as to
which Licensee is the owner pursuant to Section 3.3 hereof.

            1.3 "Net Sales" shall mean gross invoiced price for Licensed
Products sold by Licensee or its Affiliates to a Third Party, after deduction of
(i) all customary trade and quantity discounts actually allowed, (ii) allowance
for credits and returns, and (iii) sales, purchase or turnover taxes (if any).
In the event a Licensed Product is sold in combination with one or more
components which are not Licensed Products, Net Sales, for purposes of
determining royalties on such combination sale, will be calculated by
multiplying Net Sales of the combination by the fraction A/(A+B), in which A is
the gross invoiced price of the Licensed Product if sold separately and B is the
invoiced price of the other components in the combination if sold separately. If
the Licensed Products and the other components in the combination are not sold
separately, then Net Sales will be calculated based upon the gross invoiced
price of the combination less (x) the foregoing discounts, allowances and
taxes, if any, and (y) the direct cost of manufacturing the


                                       3
<PAGE>

components that are not Licensed Products. For purposes of this definition as
used throughout this Agreement, and as used in this Section 1.3, any Sublicensee
which sells Licensed Products shall be deemed an Affiliate of Licensee and not a
Third Party. For the avoidance of doubt, subject to the immediately preceding
sentence, Net Sales includes sales of Licensed Products by any Sublicensee to a
Third Party. Unless otherwise required by United Stated generally accepted
accounting principles, "Net Sales" of a Licensed Product shall be recognized on
the earlier of the date of issuance of an invoice in respect of such sale, or
the date of shipment of such Licensed Product, to a Third Party, in either case
by Licensee, its Affiliates or any Sublicensee.

            1.4 "Technology" shall mean and collectively include (i) any and all
inventions, formulas, methods, know-how, plans, processes and products, whether
patentable or not or confidential or not, developed, conceived, discovered or
reduced to practice by or on behalf of PAA, any PAA Principal or their
respective Affiliates, on or before the Effective Date, including, without
limitation, any and all of the foregoing relating to the Patent Application, and
(ii) all tangible work in progress and tangible research materials, including,
without limitation, notebooks, samples, experimental and test results, technical
and non-technical data and specifications, characteristics and designs, whether
patentable or not or confidential or not, relating to the foregoing.

            1.5 "Patent Application" shall mean the United States Patent
Application, together with its related continuations-in-part and counterpart
foreign patent filings, as listed on Exhibit A attached hereto.


                                       4
<PAGE>

            1.6 "Patent Rights" shall mean any and all rights arising from any
and all of the following:

            (a)   United States and foreign patents and/or patent applications
                  derived from or arising out of the Technology, PAA
                  Developments or Work Product (as defined in Section 3.3)
                  including, without limitation, the Patent Application;

            (b)   United States and foreign patents issued from the applications
                  described in (a) above and from divisions, continuations and
                  continuations-in-part of such applications; and

            (c)   any reissues, re-examinations or extensions of the patents and
                  applications described in (a) or (b) above.

            1.7 "Licensed Product" shall mean any product or part thereof in the
Field of Use which (i) is covered in whole or in part by a Valid Claim in the
country in which any such product or part thereof is made, used, sold or
imported; or (ii) embodies, incorporates, is based upon or derived from, or is
manufactured using a Licensed Process.

            1.8 "Licensed Product Launch" in a country shall mean the first
commercial sale (i.e., not for development purposes or in connection with the
obtaining of regulatory approval) of Licensed Product in such a country by
Licensee, its Affiliates, or any Sublicensee to a Third Party subsequent to
regulatory approval of such sale in such country.

            1.9 "Licensed Process" shall mean any method, formula, formulation,
plan or process (including manufacturing process) in the Field of Use (i) which
is covered in whole or in part by a Valid Claim in the country in which such
method, formula,


                                       5
<PAGE>

formulation, plan or process is used or practiced or (ii) which embodies,
incorporates or is based upon or derived from the Technology or the PAA
Developments.

            1.10 "Field of Use" shall mean the management or treatment of any
type of pain or muscular or skeletal discomfort arising from any cause,
including without limitation trauma, diseases such as diabetes, herpes zoster,
arthritis, osteoporosis, cancer, chemotherapy or chemical injury.

            1.11 "Third Party" shall mean any person or entity other than PAA, a
PAA Principal, Licensee and their respective Affiliates, subject, however, to
Section 1.3.

            1.12 "Valid Claim" means a claim within a Patent Right contained in
any (i) unexpired and issued patent that has not been dedicated to the public,
disclaimed, revoked or held invalid by a final unappealable decision or
unappealed decision of a court of competent jurisdiction, or (ii) pending patent
application which has been on file with the applicable patent office for seven
(7) years or less from the date on which the patent application was filed.

            1.13 "IND" shall mean an Investigational New Drug Application or
foreign equivalent.

            1.14 "Sublicensee" shall mean any direct or indirect grantee of any
or all rights granted to Licensee hereunder.

            1.15 "PAA Developments" shall mean any and all Developments created
by or on behalf of PAA.


                                       6
<PAGE>

            1.16 "Licensee Developments" shall mean any and all Developments
created by or on behalf of Licensee.

            1.17 As used herein, unless the context clearly indicates otherwise,
(i) the singular includes the plural and the plural includes the singular; and
(ii) the conjunctive includes the disjunctive and the disjunctive includes the
conjunctive.

                              2 - GRANT OF LICENSE

            2.1 PAA hereby grants to Licensee a worldwide, exclusive (even as
against PAA, subject to Section 2.2) license, with the right to grant
sublicenses, to use the Technology and Developments, to practice under the
Patent Rights, and to make, have made, use, have used, develop, have developed,
offer for sale, sell, have sold, market, have marketed, import and have
imported, Licensed Products, and to use or practice the Licensed Processes, in
each case in the Field of Use. Without limitation of the foregoing, each party
acknowledges and agrees that Licensee shall have the exclusive right for the
duration of the license rights granted pursuant to this Agreement to engage in
development activities with respect to the Technology or any Licensed Product
or Licensed Process, in each case in the Field of Use, and that neither PAA nor
any PAA Principal or their respective Affiliates will engage in any such
development activity, except pursuant to Section 3.3 hereof or a separate
agreement in writing between the parties.

            2.2 PAA and each PAA Principal hereby agrees not to grant any other
license with respect to the Technology, the Patent Rights, the Licensed Products
or the Licensed Processes, except that PAA may grant (i) non-conflicting
licenses (with the


                                       7
<PAGE>

right to grant sublicenses) having terms consistent with this Agreement in the
Technology, Patent Rights and PAA Developments, in each case outside the Field
of Use and (ii) licenses (without the right to grant sublicenses) to each of the
PAA Principals, to use the Technology and PAA Developments and to practice under
the Patent Rights, to use Licensed Products, and to use or practice the Licensed
Processes, in each case in the Field of Use solely for the therapeutic treatment
of individual patients (current or future) in the ordinary course of such PAA
Principal's clinical practice substantially as currently conducted; provided,
however, that (x) Licensee shall have no obligation to provide PAA or any PAA
Principal with any Licensed Products or any documentation or other materials
relating to the Technology, Licensed Products, Licensed Processes or
Developments, except as expressly set forth herein and (y) neither PAA nor any
PAA Principal shall in connection with the exercise of the rights granted under
subsection (ii) represent that it is in any manner affiliated or associated with
Licensee or any Affiliate or Sublicensee and (z) neither PAA nor any PAA
Principal shall in connection with the rights granted under subsection (ii) make
use of any clinical data owned or developed by or on behalf of Licensee or its
Affiliates or Sublicensees. Any and all licenses (or sublicenses) granted
pursuant to this Section 2.2 shall be in writing and shall be submitted for and
subject to Licensee's prior review and written approval, which approval shall
not be withheld unless Licensee determines, in its reasonable judgment, that the
terms of such license (or sublicense) conflict with the terms of this Agreement.
The terms of any such license granted pursuant to clause (i) of this Section 2.2
shall require (and PAA or


                                       8
<PAGE>

the licensing PAA Principal, as applicable, shall enforce such requirement) that
any sublicense, if permitted by such license, shall be subject to prior review
by and written approval of Licensee as provided in this Section 2.2. Licensee
agrees to enter into a reasonable written confidentiality agreement prior to the
disclosure of a license or sublicense for review pursuant to this Section 2.2.

            2.3 PAA and each PAA Principal acknowledges and agrees that it has,
and will have, no rights of any kind with respect to any intellectual property
or work product of any kind owned or created by Licensee in connection with the
development of Licensed Products or otherwise, including without limitation any
Licensee Developments, except as separately agreed in writing by the parties.

            2.4 Each party shall retain all right, title and interest in, and no
license is granted hereunder with respect to, any trademarks, trade names, logos
or similar identifying marks used by it in connection with any Licensed
Products or Licensed Processes, except that Licensee may state that it is
licensed by PAA to the extent provided herein.

            2.5 Any and all sublicenses (including sublicenses granted by any
Affiliate of Licensee or any Sublicensee) granted pursuant to Section 2.1 hereof
shall be in writing and shall be consistent with the terms of this Agreement.
Copies of any and all such sublicenses shall be made available for review by
PAA, subject to PAA's entering into a confidentiality agreement on terms
reasonably satisfactory to Licensee (or the relevant Affiliate of Licensee or
Sublicensee) prior to any such review.

                      3 - DEVELOPMENT AND COMMERCIALIZATION


                                       9
<PAGE>

            3.1 Licensee, at its own cost and expense, shall use commercially
reasonable efforts to bring one or more Licensed Products to market through a
diligent clinical development and commercialization program; provided that
Licensee shall be deemed to have satisfied its obligations under this Section
3.1 if its uses efforts consistent with those which it would use for a product
owned by it which evidences substantially similar clinical and commercial
promise, taking into account Licensee's capital resources and other development
and commercialization commitments and programs.

            3.2 Licensee shall have the sole right, in its own name and at its
own expense, to make any and all regulatory filings and submissions relating to
the development and commercialization of Licensed Products or Licensed
Processes in the Field of Use, including without limitation any IND filings.

            3.3 During the term of this Agreement, PAA, through one or more PAA
Principals, shall provide reasonable consulting services as requested by
Licensee with respect to the Technology and the development of Licensed Products
and Licensed Processes. Such consulting services shall include, without
limitation, disclosing to Licensee all information known by or otherwise in the
possession of PAA or any PAA Principal with respect to any and all aspects of
the Technology, Developments, Licensed Products or Licensed Processes; provided,
however, that no PAA Principal shall be obligated to provide such consulting
services for more than two days in any one month. Such consulting services shall
be compensated at the rate of $** per day or $** per half day, plus
reimbursement for reasonable, documented travel (coach class) and lodging


                                       10
<PAGE>

expenses. The parties agree that Licensee shall own all right, title and
interest in and to any and all inventions, discoveries, intellectual property
and work product resulting from the performance of such consulting services
(including any of the foregoing conceived or discovered by PAA, any PAA
Principal or their respective Affiliates, but excluding intellectual property
claimed in the Patent Application as in effect on the Effective Date or
otherwise disclosed in writing to Licensee by PAA on or prior to the Effective
Date) (collectively, the "Work Product"). For the avoidance of doubt, to the
extent that any Patent Rights arise from the Work Product, Licensee shall pay
royalties as set forth in Article 4 based upon Net Sales of Licensed Products
covered by a Valid Claim that is within such Patent Rights. Licensee shall
grant, and hereby does grant, to PAA a perpetual, non-exclusive, worldwide,
royalty-free, unlimited license, including the right to grant sublicenses, in
Licensee's rights in the Work Product outside the Field of Use. PAA and each PAA
Principal shall execute and deliver to Licensee such instruments of assignment,
releases or other documents as Licensee may request to effect or confirm
Licensee's ownership of the Work Product.

                                4 - CONSIDERATION

            4.1 In order to induce PAA to enter into this Agreement, and in
consideration of the rights and license granted hereunder, subject to the
further provisions of this Article 4, Licensee shall pay or cause to be paid
royalties to PAA during the term of this Agreement as follows:

            (a)   a license issuance fee of ** ($**), which shall be deemed
                  earned and due immediately upon the Effective Date;


                                       11
<PAGE>

            (b)   **% of annual Net Sales up to $**;

            (c)   **% of annual Net Sales between $** and $**;

            (d)   **% of annual Net Sales in excess of $**.

            4.2 The royalty percentages set forth in Section 4.1 shall each be
reduced by ** (so that **% shall instead be **%, **% shall instead be **% and
**% shall instead be **%) at any time and in any country in which Licensee's,
its Affiliates, or any Sublicensees' making, having made, using, having used,
offering for sale, selling or having sold, marketing or having marketed or
importing or having imported a Licensed Product in such country without a
license or sublicense, as applicable, would not infringe a Valid Claim in that
country or a Valid Claim in the country where such Licensed Product is made or a
Valid Claim in the country where such Licensed Product is sold or used. In
addition, Licensee shall be entitled to reduce any royalties owed by it pursuant
to Section 4.1 by an amount equal to the sum of (i) any royalty or other
payments required to be paid by Licensee to any Third Party in order to use,
develop, manufacture or sell any Licensed Product or use or practice the
Technology or any Licensed Process as contemplated hereunder, whether in
connection with settlement of a third-party claim of infringement or otherwise,
and (ii) any and all damages, costs and expenses (including, without limitation,
reasonable attorneys' fees) incurred by Licensee in connection with the defense
of any claim that the intellectual property licensed by it from PAA hereunder
infringes any Third Party's rights, to the extent that such costs are not paid
to Licensee pursuant to the indemnification obligation set forth in Section 8.3
below. Notwithstand-


                                       12
<PAGE>

ing the foregoing, Licensee shall not be entitled to reduce royalties owed
pursuant to Section 4.1 as provided for in this Section 4.2 by more than **
percent (**%) in any quarter, with any amounts by which Licensee would have been
entitled to reduce royalties owed hereunder but for the reaching of such limit
("Unutilized Amounts") being carried forward to future reporting periods. Within
thirty (30) days after the expiration of Licensee's royalty obligation with
respect to a particular country pursuant to Section 4.4, PAA shall reimburse
Licensee in an amount equal to the cumulative Unutilized Amounts for such
country.

            4.3 (i) Royalty payments hereunder are due and payable and shall be
made quarterly, in arrears, within sixty (60) days after the end of each
calendar quarter in which the royalty accrues. All royalty payments shall be in
United States funds. The exchange rate applied, if applicable, shall be the
exchange rate published in the Wall Street Journal on the last business day of
the calendar quarter in which the royalty accrued. Royalty payments shall be
made to PAA by wire transfer to a bank account designated in writing, and shall
be accompanied by mailing to PAA a report, certified to be true and correct by
an officer of Licensee, setting forth, in reasonable detail, the basis on which
such royalty payment was calculated.

      (ii) Royalties in respect of any Net Sales shall accrue at the time of
recognition of such Net Sales as provided in Section 1.3. In no event shall a
royalty be paid on an individual unit of Licensed Product more than once.


                                       13
<PAGE>

      (iii) Licensee shall be responsible for payment to PAA of royalties
accruing on Net Sales by an Affiliate or Sublicensee regardless of whether such
Affiliate or Sublicensee meets its royalty and other obligations, if any, to
Licensee.

      (iv) Licensee agrees to pay interest to PAA on the amount of any
underpayment of royalties from the date payment was due until the date payment
is made. The applicable interest rate will be the average prime rate as
published in the Wall Street Journal plus three percent (3%) during such time.

      (v) In the event Licensee asserts any monetary claim against PAA or any
PAA Principal, PAA hereby agrees and acknowledges that Licensee shall have the
right to set off against any royalty payment when due any amount claimed by
Licensee against PAA or such PAA Principal.

            4.4 The duration of payment of royalties under this Article 4 in any
country shall continue for the longer of (i) ten (10) years from Licensed
Product Launch in that country or (ii) the date of the last to expire Valid
Claim which, except for the license granted hereby, would be infringed by
Licensee making, having made, using, having used, offering for sale or selling
or having offered for sale or sold, marketing or having marketed, or importing
or having imported, Licensed Product in that country. In the case of trade
secrets deemed to be Valid Claims pursuant to Section 5.2, the duration of
payment of royalties shall be as set forth in clause (i) of this Section 4.4.
Licensee's license granted hereunder shall continue in full force and effect and
shall be fully paid up


                                       14
<PAGE>

and royalty free in any country where royalty obligations as provided for in
this Section 4.4 have expired.

            4.5 (i) Licensee shall at all times during the term of this
Agreement keep accurate books of account, and maintain supporting documents,
which show the royalties to which PAA is entitled under this Agreement
(including royalties based upon Net Sales by Affiliates of Licensee and by
Sublicensees). Said books of account and supporting documentation, which shall
be retained by Licensee for at least two (2) years after any termination of this
Agreement, shall be open for audit and inspection during the term of this
Agreement and for a period of two (2) years after any termination of this
Agreement upon reasonable prior written notice by an independent certified
public accountant chosen by PAA and reasonably acceptable to Licensee, at PAA's
expense (except as hereinafter provided with respect to the expense of an audit
and inspection). Such certified public accountant shall have the right to audit
and inspect the books of account and supporting documentation of Licensee in
order to ensure compliance with Licensee's royalty obligations hereunder and
shall, upon execution of a confidentiality agreement on terms reasonably
acceptable to Licensee, have the right to make copies and extracts of said books
of account and supporting documentation and to prepare a written report
(including any such copies or extracts) detailing the results of the audit and
inspection and deliver such written report to PAA and PAA's financial advisors
and attorneys. Audits and inspections shall not take place more than once in
each calendar year and shall be limited


                                       15
<PAGE>

to royalty obligations accruing not more than three (3) years prior to the date
of the audit and inspection.

      (ii) In the event that an audit and inspection reveals that Licensee has
underpaid any royalty due PAA under this Agreement, PAA shall provide Licensee
with written notice of such underpayment and, in addition to any other available
remedy PAA may have, Licensee shall forthwith remit such underpayment to PAA in
the manner prescribed in subsection (i) of Section 4.3 with interest calculated
in accordance with subsection (iv) of Section 4.3. In the event that an audit
and inspection reveal that Licensee has under paid royalties due under this
Agreement by an amount exceeding ten percent (10%) in any twelve (12) month
period, PAA shall provide Licensee with written notice thereof, and in addition
to Licensee's obligation to remit payment in accordance with the preceding
clause (iv) and in addition to any other available remedy PAA may have, the cost
of such audit and inspection shall be payable by Licensee.

            4.6 In the event that Licensee elects, in its sole discretion, to
file an IND in its own name with respect to a Licensed Product, Licensee
shall pay to PAA the sum of fifty thousand dollars ($50,000) within sixty
(60) days of such filing.

                             5 - PATENT PROSECUTION

            5.1 During the term of this Agreement, Licensee shall have the sole
initial right (i) to file such United States and/or foreign patent applications
covering patentable inventions included within the Technology or any
Developments created by or on behalf of PAA as Licensee shall, in its sole
discretion, deem advisable, (ii) to prosecute and


                                       16
<PAGE>

defend all patent applications referred to in clause (i), and (iii) to maintain
in force any patents resulting from such applications. Licensee shall bear all
costs associated with the foregoing filing, prosecution, defense and
maintenance incurred after the Effective Date. Without limitation of the
foregoing, Licensee shall prosecute with reasonable diligence and at its sole
expense the Patent Application, except that Licensee shall not be obligated to
prosecute any divisional resulting from the Patent Application if such
divisional does not include at least one claim with substantial application in
the Field of Use, as determined by Licensee in its reasonable discretion.

            5.2 If Licensee determines not to file any such patent application
after request by PAA, or not to prosecute any such patent application or to
maintain any such patents, Licensee shall timely provide PAA with written notice
of such determination, in which event PAA shall have the right to file or
prosecute such application or maintain such patents entirely at its own expense,
unless Licensee has a reasonable basis for such determination (including,
without limitation, Licensee's preference for keeping the relevant Technology or
Development a trade secret). Licensee's written notice of such determination
shall state the reasonable basis. If the reasonable basis is Licensee's
preference for keeping the relevant Technology or Development a trade secret,
the trade secret shall be identified in the written notice and such Trade Secret
shall become a Valid Claim for purposes of this Agreement. It shall be
unreasonable for Licensee to prefer to keep any Technology or Development a
trade secret if such Technology or Development is not material to the Field of
Use.


                                       17
<PAGE>

            5.3 Each party shall (i) timely advise the other in writing of its
intentions with respect to the filing, prosecution and maintenance of patent
applications and patents as set forth above in order to allow the other the
opportunity to comment thereon, which comments the party shall consider in good
faith, and (ii) at its own expense, provide the other with reasonable assistance
to facilitate the filing, prosecution and maintenance of patent applications and
patents as set forth above, and shall execute all documents which the other
party reasonably deems necessary or desirable therefor. Without limitation of
the foregoing clause (ii), PAA shall, within seven (7) days of the Effective
Date, cause to be delivered to Licensee all prosecution file history and other
documents relating to the Patent Application.

                          6 - THIRD-PARTY INFRINGEMENT

            6.1 Each party shall inform the other promptly in writing if it
becomes aware of any (i) applications for a patent or issued patent that may
conflict with either party's intellectual property rights hereunder or (ii) acts
of infringement or unfair competition by any third party involving such
intellectual property rights, and shall provide the other with any evidence
thereof in its possession or control.

            6.2 During the term of this Agreement, Licensee shall have the
right, but not the obligation, to prosecute and to settle any and all
infringement actions involving the Technology, Developments and/or the Patent
Rights in the Field of Use, provided that if the settlement, consent judgment or
other voluntary final disposition of any such action would affect the rights of
PAA outside the Field of Use, PAA's consent to such settlement


                                       18
<PAGE>

shall be required, such consent not to be unreasonably withheld. In furtherance
of the foregoing right, PAA hereby agrees that PAA will, at Licensee's request
and expense, join as a party plaintiff in any such infringement action. Licensee
shall keep PAA reasonably informed of the litigation strategy and of the status
of the litigation in any such infringement action and consider in good faith
PAA's comments. The entire cost of any such infringement action prosecuted by
Licensee shall be borne by Licensee, and Licensee shall keep any damages and
costs recovered in connection therewith.

            6.3 If within six (6) months after having been notified of any
alleged infringement, Licensee shall have been unsuccessful in persuading the
alleged infringer to desist and shall not have brought and shall not be
diligently prosecuting an infringement action, or if Licensee shall notify PAA
at any time prior thereto of its intention not to bring suit against any such
alleged infringer in the Field of Use, then, and in those events only, PAA shall
have the right, but not the obligation, to prosecute at its own cost and expense
any infringement action involving the Patent Rights, and PAA may, for such
purposes, join Licensee as a plaintiff as necessary to maintain standing. No
settlement, consent judgment or other voluntary final disposition of any such
action may be entered into without the consent of Licensee, which consent shall
not be unreasonably withheld. PAA shall keep any damages and costs recovered in
connection with its prosecution of an infringement action pursuant to this
Section 6.3.

            6.4 In any action brought by either party in accordance with the
foregoing, the other party shall, at the request and expense of the party
bringing such suit,


                                       19
<PAGE>

cooperate in all respects, including, to the extent possible, by having its
employees testify when requested and making available relevant records, papers,
information, samples, specimens, and the like.

                              7 - PRODUCT LIABILITY

      Licensee shall at all times during the term of this Agreement and
thereafter indemnify, defend and hold harmless PAA, its members, stockholders,
directors, officers, employees and Affiliates, and each PAA Principal
(collectively, "Indemnified Persons") against all claims, proceedings, demands
and liabilities of any kind whatsoever, including legal expenses and reasonable
attorneys' fees, arising out of (i) the death of or injury to any person or
persons or out of any damage to property resulting from Licensee's, or any
Affiliate's or Sublicensee's use of the Technology or Developments, practicing
under the Patent Rights, making or having made, using or having used, offering
for sale or selling or having sold, marketing or having marketed or importing or
having imported, any product, or using or practicing any process, except where
attributable to the gross negligence or willful misconduct of any Indemnified
Person.

               8 - REPRESENTATIONS AND WARRANTIES; INDEMNIFICATION

            8.1 PAA and each of the PAA Principals, jointly and severally,
represent and warrant to Licensee as follows:

                  (i) Except to the extent licensed to Licensee hereby, as of
      the Effective Date PAA owns the entire right, title and interest in and to
      all intellectual property licensed to Licensee hereunder (the entire
      right, title


                                       20
<PAGE>

      and interest of each of the PAA Principals therein having been duly,
      validly and effectively assigned to PAA pursuant to instruments of
      assignment, copies of which have previously been delivered to Licensee),
      and PAA has all required right, power and authority to grant the licenses
      granted hereunder.

                  (ii) To the best knowledge of PAA and each of the PAA
      Principals, the Technology, Patent Rights and any PAA Developments in
      existence as of the Effective Date do not and will not infringe any third-
      party intellectual property rights when used in accordance with this
      Agreement.

                  (iii) Except as set forth on Exhibit B hereto, there are no
      outstanding options, licenses or agreements of any kind, as of the
      Effective Date, between PAA, any PAA Principal or any Affiliate thereof
      and any Third Party relating to the Technology, the Patent Rights or any
      Licensed Product or Licensed Process.

                  (vi) To the best knowledge of PAA and each of the PAA
      Principals, as of the Effective Date, there is and has been no
      unauthorized use, infringement or misappropriation of any of PAA's
      intellectual property rights in the Technology or the Patent Rights by
      any person or entity.

                  (v) To the best knowledge of PAA and each of the PAA
      Principals, as of the Effective Date, (A) all data describing clinical
      obser-


                                       21
<PAGE>

      vations relating to the Technology or any Licensed Product or Licensed
      Process prepared by or on behalf of PAA or any PAA Principal and
      previously delivered to Licensee are true and correct in all material
      respects, and (B) Licensee has been provided with all material information
      in the possession or control of PAA, any PAA Principal or any Affiliate
      thereof which is reasonably believed by them to be material to Licensee
      entering into this Agreement, and such information does not knowingly
      contain any untrue statement of material fact or knowingly omit to state
      any material fact.

            8.2 Each party represents and warrants to the other parties that (i)
it has the full right, power and authority to enter into this Agreement and to
perform its obligations hereunder, (ii) the execution of this Agreement and the
performance of its obligations hereunder does not and will not conflict with or
result in a breach (including with the passage of time) of any other agreement
to which it is a party, and (iii) this Agreement has been duly executed and
delivered by such party and constitutes the valid and binding agreement of such
party, enforceable against such party in accordance with its terms.

            8.3 PAA and the PAA Principals, jointly and severally, on the one
hand, and Licensee, on the other, shall indemnify and hold harmless the other
against any loss, damages or expense (including, without limitation, reasonable
attorneys' fees) resulting


                                       22
<PAGE>

from any breach of this agreement by such party, including without limitation
any of the representations and warranties of such party contained herein.

            8.4 EXCEPT AS OTHERWISE EXPRESSLY SET FORTH IN THIS AGREEMENT, PAA,
ITS MEMBERS, DIRECTORS, OFFICERS, EMPLOYEES, AND AFFILIATES AND EACH PAA
PRINCIPAL MAKE NO REPRESENTATIONS AND EXTEND NO WARRANTIES OF ANY KIND, EITHER
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO WARRANTIES OF MERCHANT
ABILITY, FITNESS FOR A PARTICULAR PURPOSE, VALIDITY OF PATENT RIGHTS CLAIMS,
ISSUED OR PENDING, AND THE ABSENCE OF LATENT OR OTHER DEFECTS, WHETHER OR NOT
DISCOVERABLE OR THAT THE SUBJECT MATTER LICENSED HEREIN CAN BE SUCCESSFULLY
COMMERCIALIZED.

            8.5 IN NO EVENT SHALL A PARTY BE LIABLE HEREUNDER FOR INCIDENTAL OR
CONSEQUENTIAL OR PUNITIVE DAMAGES OF ANY KIND, INCLUDING ECONOMIC DAMAGE OR
INJURY TO PROPERTY AND LOST PROFITS, REGARDLESS OF WHETHER THE PARTY SHALL BE
ADVISED, SHALL HAVE OTHER REASON TO KNOW, OR IN FACT SHALL KNOW OF THE
POSSIBILITY OF SUCH DAMAGES.

            8.6 PAA and the PAA Principals, jointly and severally, represent and
warrant to, and covenant and agree with, Licensee, that (i) PAA has in place
with each PAA Principal, and will require as a condition of employment of each
PAA employee, agreements assigning to PAA all rights to inventions and other
intellectual property which relate to the Technology and any Developments,
Licensed Product or Licensed Process as are created or discovered by each such
PAA Principal or PAA employee, in the case of each PAA Principal, while a member
of PAA, and, in the case of each PAA employee, while employed by PAA, and (ii)
neither PAA nor any PAA Principal has entered, or will enter, into any agreement
inconsistent with the foregoing.


                                       23
<PAGE>

                                 9 - ASSIGNMENT

            Neither party may assign this Agreement or its rights and
obligations hereunder without the prior, written consent of the other party,
such consent not to be unreasonably withheld; provided, however, that (i) the
foregoing shall not limit or impair in any manner Licensee's right to grant
sublicenses as provided herein, (ii) Licensee may assign this Agreement or its
rights hereunder to an entity which acquires, by sublicense or otherwise, rights
to Licensed Products (provided that in such event Licensee shall continue to be
obligated to perform Licensee's obligations hereunder), and (iii) Licensee or
PAA may assign this Agreement and its rights hereunder to an entity which
acquires or acquires control of its entire business or that part of its business
to which this Agreement relates, whether pursuant to a merger, consolidation,
stock purchase, recapitalization, asset sale or otherwise (provided that in any
such event, Licensee or the successor entity or PAA or the successor entity in
such transaction shall continue to be liable to perform Licensee's or PAA's
obligations hereunder, as the case may be. This Agreement shall inure to the
benefit of and be binding upon the parties and their respective heirs,
executors, administrators, successors and permitted assigns. Notwithstanding any
assignment or anything in the foregoing to the contrary, PAA shall be and remain
solely liable under Section 3.3 hereof.


                                       24
<PAGE>

                            10 - TERM AND TERMINATION

            10.1 The term of this Agreement shall commence on the Effective Date
and, unless sooner terminated as provided in this Article 10, shall expire on a
country-by-country basis on the expiration of Licensee's royalty payment
obligations as provided in Section 4.5.

            10.2 Licensee shall have the right to terminate this Agreement on a
country-by-country basis or in its entirety at any time (for any reason or no
reason) by providing PAA with at least sixty (60) days prior written notice of
termination, such termination to become effective at the expiration of such
sixty (60) day period or such later date as may be specified in such notice.

            10.3 In the event a material breach of this Agreement (including,
without limitation, a material breach of any representation or warranty
contained in Article 8 hereof) by PAA or any PAA Principal on the one hand, or
Licensee on the other, the non-breaching party shall have the right to
terminate this Agreement by providing written notice of such termination to the
breaching party, but only if (i) the non-breaching party shall first have
provided the breaching party with written notice of such breach, specifying the
nature of such breach ("Breach Notice"), (ii) either (A) such breach, by its
nature, cannot be cured within ninety (90) days after receipt of such Breach
Notice or (B) if such breach is curable within such ninety (90) day period, the
breaching party fails to cure such breach within such ninety (90) day period and
(iii) such breach, either alone or in


                                       25
<PAGE>

combination with other uncured breaches as to which Breach Notice has been
given, materially impairs the value of the Agreement as a whole to the
non-breaching party.

            10.4 In the event of termination of this Agreement by Licensee under
Section 10.2 or by PAA under Section 10.3 or 10.8, (i) all licenses granted by
PAA to Licensee hereunder shall terminate, and (ii) at the request of PAA,
Licensee shall assign to PAA all regulatory filings, regulatory approvals and
clinical data owned and controlled by Licensee, and shall deliver to PAA all
documentation in its possession, relating to Licensed Products, Licensed
Processes or any Technology, or, to the extent such assignment is not legally
permissible, Licensee shall grant PAA the right to access, use and cross
reference such filings, approval and data. In the event of termination of this
Agreement by Licensee under Section 10.2, then PAA shall pay Licensee a royalty
upon any sales of Licensed Product which are made by or on behalf of PAA, its
Affiliates or any licensee or sublicensee (or sub-sublicensee) thereof after the
effective date of such termination. The amount of such royalty shall be
consistent with industry standards and shall be determined by mutual agreement
of PAA and Licensee after good faith negotiations; provided, however, that if
PAA and Licensee are unable to reach mutual agreement thereon, the matter shall
be submitted to arbitration generally in accordance with the procedures set
forth in Article 13 of this Agreement, and the arbitrator shall base his/her
decision on the following factors: (i) the value of any assigned filings,
approvals and/or data to the development and commercialization of the Licensed
Product; and (ii) the


                                       26
<PAGE>

relative contributions of the parties to the development and commercialization
of the Licensed Product.

            10.5 In the event of termination of the Agreement by Licensee under
Section 10.3, the rights and licenses granted by PAA to Licensee under this
Agreement shall, at Licensee's option, remain in effect, except that such rights
and licenses shall be on a royalty-free basis.

            10.6 Upon termination of this Agreement for any reason, nothing
herein shall be construed to release either party from performance of any
obligation incurred or liability or payment accrued prior to the effective date
of such termination, and such termination shall be without prejudice to any
remedy that any party may have in addition to those rights as provided under
this Agreement. Articles 7 and 8, this Article 10, Article 11 and Articles 12
through 14 (with respect to such Articles 12 through 14, solely to the extent
applicable to provisions, rights or obligations which survive termination) shall
survive any such termination. Licensee and any permitted Sublicensees may,
however, after the effective date of any such termination, sell any and all
Licensed Products in inventory, and complete and sell any and all Licensed
Products in the process of manufacture, at the effective date of such
termination for a period of one year after the effective date of such
termination, subject to payment of royalties to PAA as herein provided.

            10.7 In the event of termination of this Agreement by Licensee
pursuant to Section 10.3, any and all sublicenses to which a Sublicensee is a
party and which is in


                                       27
<PAGE>

effect as of the effective date of such termination shall continue in full force
and effect, provided that such Sublicensee timely pays all royalties on Net
Sales by such Sublicensee directly to PAA and continues to comply with the other
terms of such sublicense. In the event of termination of the Agreement by either
party for any other reason, any Sublicensee hereunder not then in default shall
have the right to seek a license under reasonable terms and conditions from PAA,
which license PAA agrees to negotiate in good faith.

            10.8 In the event that Licensee does not file an IND within three
(3) years of the Effective Date of this Agreement, PAA shall have the right to
terminate this Agreement upon thirty (30) days written notice to Licensee.

            10.9 In the event that Licensee alleges in a proceeding in a court
or tribunal of competent jurisdiction or in an arbitration that any patent or
patent claim within the Patent Rights is invalid or unenforceable, PAA shall
have the right to terminate this Agreement upon thirty (30) days written notice
to Licensee.

                                11 - INFORMATION

            11.1 As a result of the exercise of the rights and performance of
the obligations under this Agreement, each party (the "disclosing party") may
disclose to the other party (the "receiving party"), or the receiving party may
obtain access to, proprietary and confidential information of the disclosing
party.

            11.2 Information shall be considered proprietary and confidential
only if (i) it is in written or other tangible form and is marked as being the
confidential informa-


                                       28
<PAGE>

tion of the disclosing party or (ii) if disclosed verbally, it is reduced to
written form, marked as the confidential information of the disclosing party,
and transmitted to the receiving party within one week of the verbal disclosure
(individually and collectively, "Information").

            11.3 Each party acknowledges the confidential character of the
Information and agrees that the Information is the valuable property of the
disclosing party. The receiving party agrees not to use any Information for any
purpose or disclose Information to any Third Party (other than a party's
officers, directors, members, employees, stock holders, attorneys, financial
advisors and other representatives), except as permitted by or in the
performance of this Agreement.

            11.4 PAA further agrees to take reasonable measures which are
designed to ensure the continued secrecy of Information disclosed by it to
Licensee hereunder, subject to the exceptions contained in clauses (i) and
(ii)(A) of Section 11.5; provided that for purposes of this Section 11.4, (1)
the exception contained in clause (i)(C) of Section 11.5 shall apply only if
such Information entering into the public domain was not the result of action by
PAA or a PAA Principal or was in accordance with Section 12 and (2) references
in clause (ii)(A) of Section 11.5 to the "receiving party" shall be deemed to
refer to PAA.

            11.5 The acknowledgments, agreements, and restrictions set forth in
the preceding provisions of this Article 11 shall not (i) apply to any
Information which (A) was rightfully in the receiving party's possession, as
evidenced by written records, prior


                                       29
<PAGE>

to the date of this Agreement (other than by disclosure from the disclosing
party), without similar restrictions, (B) was disclosed to the receiving party
by a Third Party (without actual knowledge of the receiving party that such
disclosure was in breach of a duty of confidentiality of such Third Party), (C)
entered into the public domain without a breach of this Agreement, or (D) the
receiving party determines in good faith must be disclosed to comply with law or
an order or request of a governmental body, or (ii) (A) prevent Licensee or PAA,
upon and subject to the terms of this Agreement, from preparing, filing,
prosecuting or maintaining any patent applications or its resulting patents
related to the Technology, Licensed Products or Licensed Processes, (B) prevent
Licensee, its Affiliates or any Sublicensee (1) from disclosing Information to
persons or entities working on their behalf or to governmental agencies, to the
extent Licensee or such other persons or entities reasonably believe is required
or desirable to secure any government approval for the development, manufacture,
marketing or sale of any Licensed Product, or (2) upon imminent approval or
actual approval for registration by a governmental agency in a country of a drug
application for any Licensed Product, from disclosing Information to the extent
reasonably necessary to promote the use, marketing or sale of Licensed Product
in that country or (C) prevent Licensee or its Affiliates from disclosing
Information which Licensee determines in good faith is required by law or
reasonably necessary in connection with any financing, strategic transaction,
acquisition or disposition involving Licensee or any Affiliate thereof.

                                12 - PUBLICATIONS


                                       30
<PAGE>

      During the term of the Agreement, the following restrictions shall apply
with respect to disclosure by PAA or any PAA Principal or Affiliate (the
"Publishing Party") in any publication or presentation, in oral or written form,
of information or data relating to the Technology (collectively,
"Publications"):

            (a)   The Publishing Party shall provide Licensee with a copy of any
                  proposed Publication at least forty-five (45) days prior to
                  submission for publication (or presentation) so as to provide
                  Licensee with the opportunity to recommend any changes it
                  deems necessary to continue to maintain the confidentiality
                  of information or data disclosed by Licensee to the Publishing
                  Party in accordance with the requirements of this Agreement.
                  The incorporation of such recommended changes shall not be
                  unreasonably refused; and

            (b)   If Licensee notifies the Publishing Party ("Notice") within
                  thirty (30) days of receipt of the copy of the proposed
                  Publication that such Publication, in its reasonable judgment
                  (i) contains an invention for which Licensee desires to (and
                  is hereunder entitled to) pursue patent protection, or (ii)
                  could be expected to have a material adverse effect on the
                  commercial value of the information or data contained therein,
                  of any Information disclosed to Licensee hereunder or of any
                  aspect of the Technology disclosed to Licensee or licensed
                  hereunder, the Publishing Party shall prevent such


                                       31
<PAGE>

                  publication (or presentation) or delay such publication (or
                  presentation) for a reasonable period of time as specified by
                  Licensee. In the case of inventions, such delay shall be for a
                  period of time sufficient to permit the timely preparation and
                  filing of a patent application or applications on the
                  invention, and in no event less than one hundred eighty (180)
                  days from the date of Notice. Any dispute or disagreement
                  under this subsection (b) may be submitted to arbitration in
                  accordance with the procedures set forth in Article 14 hereof.

                      13 - NOTICES AND OTHER COMMUNICATIONS

      Any notice or communication (including invoices) required to be given
hereunder shall be in writing and shall be considered properly given (a) on the
date delivered or sent if personally delivered against written receipt, (b) on
the date of receipt if sent by certified or registered mail, or (c) on the date
of receipt if sent by overnight mail or reputable over night courier, as
follows:

            If to PAA or any PAA Principal:

                  PHARMACEUTICAL APPLICATIONS ASSOCIATES, LLC
                  402 East Yakima Avenue, Suite 330
                  Yakima, Washington 98901-2755
                  Attn: C. Donald Williams
                  Facsimile: (509) 454-3295

or such other address (and/or facsimile number) that PAA may advise in writing
in accordance with this Article 12;


                                       32
<PAGE>

            If to Licensee:

                  PRAECIS PHARMACEUTICALS INCORPORATED
                  1 Hampshire Street
                  Cambridge, Massachusetts 02139
                  Attn.: Vice President of Corporate Development
                  Facsimile: (617) 494-8414

or such other address (and/or facsimile number) that Licensee may advise in
writing in accordance with this Article 12.

                             14 - DISPUTE RESOLUTION

            14.1 Unless otherwise explicitly set forth in this Agreement, in the
event that the parties are unable to resolve any dispute, controversy or claim
arising out of, or in relation to this Agreement, or the breach, termination or
invalidity thereof (collectively "Issue"), the parties shall first refer such
Issue to the respective Chief Executive Officers of Licensee and PAA. In the
event that such Issue cannot be resolved by these individuals after a good
faith discussion to resolve the Issue, then either party may initiate
arbitration in Boston, Massachusetts in accordance with this subsection under
the guidelines of the American Arbitration Association ("AAA") and the
commercial rules then in effect for AAA, except as otherwise provided for
herein.

            14.2 A party shall notify the other in writing should it intend to
initiate arbitration. The parties shall select, by mutual agreement, one
arbitrator within a time period of thirty (30) days after receipt of such
notice. Should no arbitrator be chosen within the above period, the AAA shall
appoint the arbitrator within thirty (30) days after the end of such period.


                                       33
<PAGE>

            14.3 Unless otherwise agreed to by the parties, the arbitrator shall
make such decision based on the following factors in descending order of
importance: (a) consistency with the provisions of this Agreement; (b)
consistency with the intent of the parties as reflected in this Agreement; and
(c) customary and reasonable provisions included in comparable agreements. The
decision of the arbitrator will be binding upon the parties without the right of
appeal, and judgment upon the decision rendered by the arbitrator may be entered
in any court having jurisdiction thereof.

            14.4 The parties shall share equally the reasonable documented cost
of such arbitration proceeding. Each party shall be responsible for its own
costs and expenses in any such arbitration proceeding.

                          15 - MISCELLANEOUS PROVISIONS

            15.1 This Agreement shall be construed, governed, interpreted and
applied in accordance with the laws of The Commonwealth of Massachusetts,
without giving effect to its conflicts of law principles, except that questions
affecting the construction and effect of any patent shall be determined by the
law of the country in which the patent was granted.

            15.2 The parties hereto acknowledge that this Agreement (including
its Exhibits) sets forth the entire Agreement and understanding of the parties
with respect to the subject matter hereof, and shall not be subject to any
change or modification except by the execution of a written instrument
subscribed to by Licensee and PAA.


                                       34
<PAGE>

            15.3 The invalidity or enforceability of any provision of this
Agreement shall not affect the validity or enforceability of any other provision
of this Agreement, each of which shall remain in full force and effect. In
addition, any such invalid or unenforceable provision shall be deemed amended or
replaced with a provision that is valid and enforceable which achieves, to the
fullest extent possible, the original objectives and intent of the parties as
reflected in the offending provision.

            15.4 Licensee agrees to mark the Licensed Products sold in the
United States with all applicable United States patent numbers. All Licensed
Products shipped to or sold in other countries shall be marked in such manner as
to conform with the patent laws and practices of the country of manufacture
and/or sale.

            15.5 The failure of either party to assert a right hereunder or to
insist upon compliance with any term or condition of this Agreement shall not
constitute a waiver of that right or excuse a subsequent failure to perform any
such term or condition by the other party.

            15.6 Nothing herein shall be deemed to constitute either party as
the agent or representative of the other party. Each party shall be an
independent contractor, not an employee or partner of the other party. Each
party shall be responsible for the conduct of activities at its own facilities
and for any liabilities resulting therefrom. Neither party shall be responsible
for the acts or omissions of the other party, and neither party will have
authority or represent to have authority to speak for, represent or obligate the
other party in any way without prior written authority from the other party.


                                       35
<PAGE>

            15.7 No party will disclose the terms or conditions of this
Agreement to any Third Party (other than a party's officers, directors, members,
employees, stockholders, attorneys, financial advisors and other
representatives) or issue any press release relating to the terms and conditions
of this Agreement for any purpose, without the prior written consent of the
other party except as required by law (including without limitation upon order
or request of any regulatory agency or commission of competent jurisdiction);
provided that such consent will not be unreasonably withheld and shall not be
required for any such disclosure by Licensee which Licensee determines in good
faith is required by law or reasonably necessary in connection with any
financing, strategic transaction, acquisition or disposition involving Licensee.
The restriction on disclosure contained herein shall not apply to any
information which is essentially identical to that contained in a previous
disclosure authorized hereunder.

            15.8 In the event that PAA shall become insolvent, shall make an
assignment for the benefit of creditors, or shall have a petition in bankruptcy
filed for or against it (which, in the case of an involuntary petition, is not
dismissed or stayed within sixty (60) days after such petition is filed), all
rights and licenses granted under or pursuant to this Agreement by PAA to
Licensee are, and shall otherwise be deemed to be, for purposes of Section
365(n) of Title 11, US Code (the "Bankruptcy Code"), licenses of rights to
"intellectual property" as defined under Section 101(60) of the Bankruptcy Code.
The parties agree that Licensee, as a licensee of such rights under this
Agreement,


                                       36
<PAGE>

shall retain and may fully exercise all of its rights and elections under the
Bankruptcy Code, subject to the continued performance of its obligations under
this Agreement.

            15.9 The waiver by a party of a breach or a default of any provision
of this Agreement by the other party shall not be construed as a waiver of any
succeeding breach of the same or any other provision, nor shall any delay or
omission on the part of a party to exercise or avail itself of any right, power
or privilege that it has or may have hereunder operate as a waiver of any right,
power or privilege by such party.

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

            15.11 Each of the parties hereto covenants and agrees that at all
times hereafter it will execute, acknowledge and deliver all such instruments
and documents which may be necessary, or with the other party may reasonably
request, to effectuate the rights and perform the obligations contemplated by
this Agreement.


                                       37
<PAGE>

            IN WITNESS WHEREOF, the parties have duly executed this Agreement as
of the day and year first written above.

                                        PRAECIS PHARMACEUTICALS
                                        INCORPORATED

                                        /s/ Mark A. Silver
                                        ----------------------------------------
                                        Mark A. Silver
                                        Vice President of Corporate Development

                                        /s/ William L. Kubasek
                                        ----------------------------------------
                                        William L. Kubasek
                                        Director of Business Development


                                        PHARMACEUTICAL APPLICATIONS
                                        ASSOCIATES LLC

                                        /s/ C. Donald Williams
                                        ----------------------------------------
                                        By:  C. Donald Williams
                                        Its: President

                                        /s/ C. Donald Williams
                                        ----------------------------------------
                                        C. Donald Williams, M.D., C.G.P.

                                        /s/ Robert Murdock
                                        ----------------------------------------
                                        Robert Murdock, R.Ph.


                                       38
<PAGE>

                                                                       EXHIBIT A

        U.S. Patent Application No. 3742-901-2-IPROV and related filings.


                                       A-1
<PAGE>

                                                                       EXHIBIT B

PAA has entered into Confidentiality Agreements with each of the following
individuals and entities:

            **
            **
            **
            **
            **
            **
            **
            **
            **
            **
            **
            **
            **
            **
            **
            **
            **
            **
            **
            **
            **
            **
            **
            **
            **
            **

PAA has not entered into any license agreements relating to the Technology, the
Patent Rights, or any Licensed Product or Licensed Process.


                                       B-1