RESTRICTED STOCK BONUS AGREEMENT
                           WITH K. PETER HIRTH, PH.D.

     THIS  AGREEMENT  is made as of the  16th  day of  September,  1997,  by and
between SUGEN, INC., a Delaware corporation (the "Company"), and K. Peter Hirth,
Ph.D. ("Recipient").


                                  WITNESSETH:

     WHEREAS, Recipient has provided valuable services to the Company;

     WHEREAS,  the Company desires to issue,  and Recipient  desires to receive,
shares of the Company's common stock ("Common Stock") in consideration  for past
services rendered to the Company or for its benefit; and

     WHEREAS,  the issuance of Common stock  hereunder is in connection with and
in furtherance of the Company's  compensatory  benefit program for participation
of the Company's employees, directors, officers, consultants and advisors.

     NOW, THEREFORE, IT IS AGREED between the parties as follows:

     1. The Company  hereby awards to Recipient  twenty-five  thousand  (25,000)
shares of Common  Stock  (the  "Shares"),  subject  to the  following  terms and
conditions.

     2.  Provided  that  Recipient  has  continuously  rendered  services to the
Company  or any  affiliate  of the  Company  from  and  after  the  date of this
Agreement  through  March 31, 1999,  the Shares shall vest in their  entirety on
March 31, 1999 (the  "Vesting  Date").  However,  to the extent the Vesting Date
occurs on a date on which the trading of the Shares  either (i) would  result in
liability  to Recipient  under Rule 10b-5 as  promulgated  under the  Securities
Exchange  Act of 1934,  as  amended,  or (ii)  would  be  prohibited  under  the
Company's  trading window policy  designed to prevent  violations of Rule 10b-5,
then the Vesting Date shall be delayed  until the first date on which  Recipient
could trade the Shares without either  incurring  liability  under Rule 10b-5 or
violating the Company's insider trading window policy.

     3. If at any time prior to the  Vesting  Date,  Recipient  ceases to render
services to the Company or any affiliate of the Company (the "Separation"),  the
Shares shall immediately cease vesting, Recipient shall have no further right in
the Shares and the Shares shall  automatically  be  reacquired by the Company at
the Current Market Price (as hereinafter  defined).  The Current Market Price of
the Company's  Common Stock shall be the closing price (or bid price if there is
no  such  closing   price)  of  the   Company's   Common  Stock  quoted  in  the
Over-The-Counter Market  Summary  or the  closing  price  quoted  on the  Nasdaq
National  Market or on the  primary  national  securities  exchange on which the
Common  Stock is then  listed,  whichever  is  applicable,  as  published in the
Western Edition of The Wall Street Journal (or, if not so reported, as otherwise
reported by the Nasdaq National  Market) on the date of Recipient's  Separation;
provided, however, that if there is no public market for the Company's Common



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Stock,  the Current Market Price shall be the fair market value of the Company's
Common Stock as determined by the Company's Board of Directors in good faith.

     4.  Recipient  may  satisfy  any  federal,  state or local tax  withholding
obligation  relating to the  acquisition  of the Shares by any of the  following
means or by a  combination  of such means:  (1)  tendering a cash  payment,  (2)
authorizing the Company to withhold shares from the Shares otherwise issuable to
Recipient as a result of the acquisition of the Shares, or (3) delivering to the
Company owned and unencumbered shares of the Common Stock of the Company.

     5.  Recipient  acknowledges  that the Shares to be issued  pursuant to this
Agreement have not been registered  under the Securities Act of 1933, as amended
(the "Securities Act"), and that the Shares are deemed to constitute "restricted
securities"  under  Rule 144  promulgated  under  the  Securities  Act.  In this
connection,  Recipient  warrants and represents to the Company that Recipient is
holding the Shares for Recipient's own account and that Recipient has no present
intention of  distributing  or selling said stock except as permitted  under the
Securities  Act.  Recipient  further  warrants and represents that Recipient has
either (i) a preexisting  personal or business  relationship with the Company or
any of its officers,  directors or controlling  persons, or (ii) the capacity to
protect his or her own interests in connection with the receipt of the Shares by
virtue of the business or financial  expertise of any  professional  advisors to
Recipient who are unaffiliated with, and who are not compensated by, the Company
or any of its affiliates, directly or indirectly. Recipient further acknowledges
that the exemption from registration under Rule 144 will not be available for at
least two (2) years from the date of acquisition of the Shares,  unless at least
one (1) year  from the date of  acquisition  (i) a public  trading  market  then
exists for the Common Stock of the Company, (ii) adequate information concerning
the Company is then available to the public and (iii) other terms and conditions
of Rule 144 are complied  with;  and that any  disposition  of the Shares may be
made only in limited amounts in accordance with such terms and conditions.

     6. Until the Vesting Date, the Shares shall be issued in book form only and
share certificates shall not be issued.  Notwithstanding  the foregoing,  in the
event  that   certificates   representing  the  Shares  are  issued,   all  such
certificates shall have endorsed thereon the following legends:

         (a) "THE  SECURITIES  REPRESENTED BY THIS  CERTIFICATE ARE UNVESTED AND
     SUBJECT  TO  FORFEITURE  IN  ACCORDANCE  WITH THE  RESTRICTED  STOCK  BONUS
     AGREEMENT BETWEEN THE ISSUER AND THE REGISTERED  HOLDER, OR THE PREDECESSOR
     IN INTEREST,  A COPY OF WHICH IS ON FILE AT THE ISSUER'S  PRINCIPAL OFFICE.
     ANY  TRANSFER  OR  ATTEMPTED  TRANSFER  OF THE SHARES  REPRESENTED  BY THIS
     CERTIFICATE  IS VOID  WITHOUT  THE PRIOR  EXPRESS  WRITTEN  CONSENT  OF THE
     ISSUER."

         (b)  "THE  SECURITIES  REPRESENTED  BY THIS  CERTIFICATE  HAVE NOT BEEN
     REGISTERED  UNDER  THE SECURITIES ACT OF 1933, AS AMENDED (THE  "SECURITIES
     ACT"). THEY MAY NOT BE SOLD OR



<PAGE>


     OFFERED  FOR  SALE OR  OTHERWISE  DISTRIBUTED  UNLESS  THE  SECURITIES  ARE
     REGISTERED   UNDER  THE  SECURITIES  ACT  OR  AN  EXEMPTION   THEREFROM  IS
     AVAILABLE."

     7. Recipient  agrees that it shall in no event make any  disposition of all
or any portion of the Shares unless and until:

         (i)  There  is  then in  effect  a  registration  statement  under  the
Securities Act covering such proposed  disposition and such  disposition is made
in accordance with said registration statement; or

         (ii) (a)  Recipient  shall have  notified  the Company of the  proposed
disposition  and shall have  furnished the Company with a derailed  statement of
the circumstances surrounding the proposed disposition, (b) Recipient shall have
furnished the Company with an opinion of its own counsel to the effect that such
disposition  will not require  registration  of the Shares under the  Securities
Act, and (c) such opinion of its counsel shall have been concurred in by counsel
for the Company,  such  concurrence  not to be  unreasonably  withheld,  and the
Company shall have advised Recipient of such concurrence.

     8. The  Company  shall not be  required  (i) to  transfer  on its books any
Shares  which shall have been sold or  transferred  in  violation  of any of the
provisions set forth in this  Agreement or the terms of the  Securities  Act, or
(ii) to treat as owner of such  Shares  or to  accord  the right to vote as such
owner or to pay dividends to any  transferee to whom such Shares shall have been
so transferred.

     9. Subject to the provisions of this Agreement, Recipient shall, during the
term of this  Agreement,  exercise all rights and privileges of a stockholder of
the  Company  with  respect to the Shares.  Recipient  shall be deemed to be the
holder of the Shares for purposes of receiving any  dividends  which may be paid
with respect to such Shares and for  purposes of  exercising  any voting  rights
relating to such Shares,  even if some or all of such Shares have not yet vested
and been released from the Company's reacquisition right.

     10. If any change is made in the Shares subject to this Agreement  (through
merger,  consolidation,   reorganization,   recapitalization,   stock  dividend,
dividend  in  property  other  than cash,  stock  split,  liquidating  dividend,
combination  of shares,  exchange of shares,  change in  corporate  structure or
otherwise),  this Agreement will be  appropriately  adjusted in the class(es) of
securities,  maximum  number of Shares  and  price  per  Share  subject  to this
Agreement.

     11. In the event of: (1) a merger or  consolidation in which the Company is
not the surviving corporation;  (2) a reverse merger in which the Company is the
surviving  corporation but the shares of the Company's Common Stock  outstanding
immediately  preceding  the merger are  converted  by virtue of the merger  into
other property,  whether in the form of securities,  cash or otherwise;  (3) any
other  capital  reorganization  in which  more than fifty  percent  (50%) of the
shares of the Company entitled to vote are exchanged; (4) a transaction or group
of related  transactions  involving the sale of all or substantially  all of the
Company's assets; (5) the acquisition by any person,  entity or group (excluding
any employee benefit plan, or related trust,



<PAGE>


sponsored or maintained by the Company or any  subsidiary of the Company) of the
beneficial  ownership,  directly or  indirectly,  of  securities  of the Company
representing  more than fifty percent (50%) of the combined  voting power in the
election of members of the board of directors of the Company; or (6) a change in
the composition of the Company's Board of Directors such that, during any period
of two  consecutive  years,  individuals  who, at the  beginning of such period,
constitute the Board of Directors,  together with  individuals  who are Approved
New Directors (as defined below), cease for any reason to have authority to cast
at least a majority of the votes which all  directors  on the Board are entitled
to vote;  then, to the extent not prohibited by law, the time during the Vesting
Date shall be accelerated  prior to such event.  For purposes of this Agreement,
an  "Approved  New  Director"  shall be a Board member  whose  election,  or the
nomination for election by the Company's stockholders, was approved by a vote of
a  majority  of the votes  entitled  to be cast by the  directors  then still in
office who were directors at the beginning of the period.

     12.  The  acquisition  and  vesting  of the  Shares  may have  adverse  tax
consequences  to the  Recipient  which may  avoided  or  mitigated  by filing an
election  under  Section  83(b) of the Internal  Revenue  Code,  as amended (the
"Code").  Such  election must be filed within thirty (30) days after the date of
this Agreement.  RECIPIENT  ACKNOWLEDGES THAT IT IS HIS OWN RESPONSIBILITY,  AND
NOT THE COMPANY'S,  TO FILE A TIMELY ELECTION UNDER CODE SECTION 83(B),  EVEN IF
RECIPIENT REQUESTS THE COMPANY TO MAKE THE FILING ON HIS OR HER BEHALF.

     13. Rights and  obligations  under this Agreement  shall not be impaired by
any amendment of this Agreement  unless (i) the Company  requests the consent of
Recipient and (ii) Recipient consents in writing.

     14. The parties  hereto agree to execute such  further  instruments  and to
take such further  action as may reasonably be necessary to carry out the intent
of this Agreement.

     15. Any notice  required or permitted  hereunder  shall be given in writing
and shall be deemed  effectively given upon personal delivery or upon deposit in
the United States Post Office,  by registered or certified mail with postage and
fees  prepaid,  addressed to the other party  hereto at its address  hereinafter
shown below its  signature or at such other  address as such party may designate
by ten (10) days' advance written notice to the other party hereto.

     16. This Agreement shall be governed by the laws of the State of California
without regard to such State's principles of conflict of laws.

     17. This Agreement shall inure to the benefit of the successors and assigns
of the Company and,  subject to the  restrictions  on transfer herein set forth,
shall be binding upon Recipient,  his or her heirs,  executors,  administrators,
successors and assigns.

     18. This Agreement does not constitute an employment  contract nor shall be
deemed to create in any way whatsoever  any  obligation on  Recipient's  part to
continue in the employ of the Company or any  affiliate  of the  Company,  or to
limit the ability of the Company or any



<PAGE>


affiliate of the Company to terminate  Recipient's  employment  with the Company
or affiliate of the Company at any time, for any reason or for no reason.

     19. This Agreement constitutes the entire, final and exclusive statement of
the  agreement  between the parties  hereto with  respect to the subject  matter
hereof.

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


RECIPIENT:                                        SUGEN, INC.:

/s/ K. Peter Hirth Ph.D                           By /s/ Stephen Evans-Freke
---------------------------                          ---------------------------
K. Peter Hirth Ph.D                                  Stephen Evans-Freke
                                                     Chief Executive Officer and
Address: ------------------                          Chairman of the Board of
                                                     Directors
---------------------------