Document:

EMPLOYMENT
                                                                 AGREEMENT dated
                                                                 as of September
                                                                 9, 2002,
                                                                 between
                                                                 SYNAPTIC
                                                                 PHARMACEUTICAL
                                                                 CORPORATION, a
                                                                 Delaware
                                                                 corporation
                                                                 (the
                                                                 "Company"), and
                                                                 Errol de Souza
                                                                 (the
                                                                 "Employee").

     Effective as of the Start Date (as defined  below),  the Employee is hereby
employed  by the Company as its Chief  Executive  Officer  and  President.  As a
result of such employment by the Company,  the Employee will possess special and
particular  knowledge of the business and  operations  of the Company and of the
industry in which it operates.  The Company and the Employee desire to set forth
in writing the terms of the Employee's employment by the Company in the capacity
of Chief Executive Officer and President.

     ACCORDINGLY,  in  consideration  of the mutual  covenants  and  obligations
hereinafter set forth, the parties hereto agree as follows:

     1.  Employment.  The Company hereby employs the Employee,  and the Employee
hereby accepts such  employment by the Company,  on the terms and subject to the
conditions hereinafter set forth.

     2. Term. Subject to earlier  termination as provided herein, the employment
of the  Employee  hereunder  shall  be  for a four  year  period  commencing  on
September 9, 2002 (the "Start Date") and ending on the fourth anniversary of the
Start Date; provided, however, that commencing as of such fourth anniversary and
on each anniversary thereafter, unless either party hereto gives the other party
at least 90 days' prior written notice of its or the Employee's  election not to
extend or further extend the period of the Employee's employment hereunder, such
period shall  automatically be extended for an additional one-year period on the
same terms and conditions set forth herein,  unless  otherwise  mutually  agreed
upon by the parties in writing.  For  convenience  of reference,  such period of
employment,  as the same may be extended or earlier terminated as aforesaid,  is
referred to herein as the "Employment Period."

     3. Duties. (a) During the Employment Period, the Employee shall be employed
as the Chief  Executive  Officer and  President of the Company and shall perform
such duties for the Company consistent with such position as may be provided for
in the By-Laws and/or  reasonably  assigned to the Employee from time to time by
the Board of Directors of the Company (the  "Board").  The Employee shall report
to the Board.  In addition,  as soon as  practicable  after the Start Date,  the
Employee  shall be  appointed  to the  Board as a member  thereof.  If the Board
determines that it is in the best interests of the Company to elect or appoint a
Chairman of the Board,  the Employee  shall be  considered  for such position in
good faith by the Board and such  candidacy  shall be reviewed in an appropriate
and serious manner.

     (b) The  Employee  shall  perform the  Employee's  duties  hereunder at the
offices of the  Company in  Paramus,  New Jersey;  provided,  however,  that the
Company may require the Employee to travel in connection with the performance of
such duties.

     (c) The Employee  represents and warrants that the  performance by Employee
of the Employee's  duties and obligations  under this Agreement will not violate
any  agreement  between the Employee and any other  person,  firm,  partnership,
corporation or other organization.

     4. Time to be Devoted to Employment.  Except for vacations and absences due
to temporary illness in accordance with the policies of the Company,  during the
Employment  Period,  the Employee  shall devote all of the  Employee's  business
time,  attention and energies to the performance of the Employee's  duties under
this Agreement.  During the Employment  Period,  the Employee shall not, without
the prior  written  consent  of the  Board,  be  engaged  in any other  business
activity which,  in the judgment of the Board,  conflicts with the duties of the
Employee under this Agreement, whether or not such activity is pursued for gain,
profit or other pecuniary advantage;  provided, however, that the Employee shall
be allowed,  to the extent such activities do not  substantially  interfere with
the performance by the Employee of his duties and responsibilities hereunder, to
(a) manage the Employee's  personal,  financial and legal affairs, and (b) serve
on the corporate, civic or charitable boards or committees set forth on Schedule
A hereto.

     5.  Compensation;  Reimbursement.  (a) Base Salary.  During the  Employment
Period,  the Company  shall pay to the  Employee a base  salary of $450,000  per
annum, subject to increase by the Board, in its sole discretion. For convenience
of reference,  such base salary,  as the same may be increased as aforesaid,  is
referred to herein as the "Base  Salary."  The Base  Salary  shall be payable in
such  installments  (but not less frequent than monthly) as is the policy of the
Company generally with respect to its executive officers.  The Base Salary shall
be reviewed annually by the Board for increases only, as determined by the Board
in its sole discretion.

     (b) Annual Performance Bonus. The Employee shall be eligible to receive for
each  calendar  year of the  Company  (or  portion  thereof)  ending  during the
Employment  Period  a cash  bonus  having a  target  amount  equal to 50% of the
Employee's Base Salary for such calendar year (or portion  thereof) and based on
and subject to the achievement of annual  performance  objectives  determined by
the Board.  Each such cash  bonus,  if earned,  will be payable to the  Employee
within  ninety days after the end of the calendar  year in respect of which such
bonus is earned.  Additional  bonuses may be approved by the Board,  in its sole
discretion. Notwithstanding the above, for calendar year 2002 only, the Employee
shall be entitled to receive,  if the Employee has not voluntarily  resigned (or
given notice thereof) prior to January 1, 2003, a guaranteed pro-rated bonus for
2002 equal to $225,000,  multiplied by a fraction, the numerator of which is the
number of days the Employee is employed by the Company  after the Start Date and
prior to January 1, 2003, and the denominator of which is 365.

     (c) Benefits.  During the Employment Period, the Employee shall be eligible
for such benefits as are generally made available to other executive officers of
the Company.

     (d) Reimbursement of Expenses.  During the Employment  Period,  the Company
shall  reimburse the Employee,  in accordance with the policies and practices of
the Company in effect from time to time during such Period,  for all  reasonable
and  necessary  traveling  expenses  and  other  disbursements  incurred  by the
Employee for or on behalf of the Company in connection  with the  performance of
the  Employee's  duties  hereunder  (such  expenses  being referred to herein as
"Reimbursable  Expenses")  upon  presentation  by the Employee to the Company of
appropriate documentation therefor.

     (e)  Option  Grants.  The  Employee  shall be granted on the Start Date two
separate  options to purchase in the  aggregate  1,000,000  shares of the Common
Stock of the Company,  $.01 par value (the "Common Stock"), at a price per share
equal to the fair market  value of the Common  Stock as of the Start  Date.  The
first,  an option to acquire  250,000  shares,  (A) shall be  granted  under and
subject to the  Company's  1996  Incentive  Plan (the "Plan") and, to the extent
permitted by law, shall be treated as an "incentive stock option" (under Section
422 of the  Internal  Revenue Code of 1986,  as amended),  and (B) shall be made
pursuant to the terms and  conditions  of the  Company's  standard form of stock
option agreement, except as modified to reflect the terms and provisions herein.
The second option, to acquire 750,000 shares, shall be granted on similar terms,
but shall not be granted under the Plan, and shall be made pursuant to the terms
and  conditions of a stock option  agreement  similar to the Company's  standard
form of stock  option  agreement,  except as  modified  to reflect the terms and
provisions herein. Each such stock option will provide,  among other things, for
pro-rata four-year vesting of the option shares covered thereby, with the option
becoming vested monthly in 48 monthly installments  beginning on the date in the
month  immediately  following  the month in which the  option  is  granted  that
corresponds  to the  actual  date grant of the  option.  The  Employee  shall be
considered  for  additional  stock  options  each year to be  determined  by the
Company's Compensation  Committee of the Board in its sole discretion.  The form
of such stock option agreements is attached hereto as Exhibit A.

     (f) Signing Bonus.  The Employee shall be entitled,  subject to the vesting
and forfeiture  conditions set forth below, to receive a one-time  signing bonus
(the "Signing  Bonus") equal to $150,000,  payable  within thirty days after the
Start Date. The Signing Bonus shall vest as to 25% of the aggregate bonus amount
on each of the first four  anniversaries  of the Start Date. In the event of the
Employee's  termination of employment  due to death,  a Disability  Termination,
Termination  Without Cause or a Resignation  For Good Reason,  the Signing Bonus
shall become 100% vested as of the date of any such termination. In the event of
the Employee's  termination for any other reason prior to the fourth anniversary
of  the  Start  Date,  any  unvested  portion  of the  Signing  Bonus  shall  be
immediately  forfeited  and  returned  in gross  amount  to the  Company  by the
Employee or the Employee's estate, beneficiaries or other legal representatives.
In addition,  the Company  shall have the right to offset the amount of any such
obligation  of the Employee  against and in reduction of any  severance or other
benefits  or  payments  which  the  Employee  (or  the   Employee's   estate  or
beneficiaries)  may otherwise be entitled to receive from the Company under this
Agreement  or  otherwise.  The  Employee  and the  Company  each  agree that the
aggregate  amount of the  Signing  Bonus  shall be  treated  for all  income and
payroll tax purposes as ordinary,  wage-type  compensation  actually received in
2002 and all tax returns and other documentation filed or issued by the Employee
and/or  the  Company  shall  reflect  and be  consistent  with  such  treatment.
Consistent with the above and to the extent  required by law or regulation,  the
Company shall report any amounts of the Signing Bonus returned to the Company by
or in respect of the Employee as ordinary income and, to the extent permitted by
applicable  law and  regulation,  the Company  shall not object to any deduction
claimed by the Employee in respect thereof.

     (g) Relocation Expenses.  The Employee shall be entitled,  to be reimbursed
by the Company  against  receipt of proper  invoices  for up to $130,000 for all
reasonable  out-of-pocket costs, including,  without limitation,  interim living
expenses, household property storage costs, real estate closing costs and income
tax  increases  attributable  to  reimbursements   hereunder,   related  to  the
relocation of the Employee (and his spouse and dependent  children) from Basking
Ridge,  New Jersey to Paramus,  New Jersey or any other township within 30 miles
of Paramus, New Jersey.

     6. Termination of Employment.

     (a) General. The Company may terminate the Employee's  employment hereunder
at any time for any reason. The Employee may terminate the Employee's employment
hereunder pursuant to a Resignation for Good Reason, a Voluntary  Termination or
a  Disability   Termination.   The   Employee's   employment   shall   terminate
automatically  upon the  Employee's  death.  Any  termination  of the Employee's
employment  is referred to herein as a  "Termination  of  Employment."  Upon the
occurrence of any  Termination  of Employment,  the Employee  shall  immediately
resign from any membership on the Board and from any committees thereof (and the
Employee  shall  promptly  tender  to the  Board a  written  resignation  letter
effecting the foregoing).

     (b)  Termination  Notice.  The  Company  or the  Employee  may  initiate  a
Termination of Employment in any manner permitted  hereunder by giving the other
party written notice thereof (the "Termination Notice").

     (c) Termination  Date. The effective date (the  "Termination  Date") of any
Termination  of  Employment  shall be  deemed to be the later of (i) the date on
which  the  Termination  Notice  is given  and (ii)  the date  specified  as the
effective date in the Termination Notice; provided, however, that in the case of
the Employee's death, the Termination Date shall be the date of death and in the
case of a Disability  Termination,  the Termination  Date shall be the thirtieth
(30th)  day after  receipt by the  Employee  or the  Company of the  Termination
Notice stating that the termination is a Disability Termination.

     7. Termination by the Company.

     (a) Termination for Cause.  Any Termination of Employment  initiated by the
Company  upon the  occurrence  of an event  that  constitutes  Cause  shall be a
"Termination for Cause." For purposes of this Agreement,  the term "Cause" shall
mean (i) the  Employee's  willful  failure  to  perform  those  duties  that the
Employee is required or expected to perform as an employee of the Company  under
Section  3  hereof  (other  than due to a  physical  disability  certified  by a
physician reasonably acceptable to the Company), (ii) the Employee's engaging in
willful  misconduct  or gross  negligence  that is  materially  injurious to the
Company,  (iii) the  Employee's  conviction of a felony,  or (iv) the Employee's
dishonesty  intended to personally enrich the Employee at the Company's expense.
In the event of a Termination  for Cause,  the  Termination  Notice given to the
Employee by the Company shall state that the  Termination  of Employment is "for
Cause." Such written notice shall specify the particular act or acts, or failure
to act,  which  is or are  the  basis  for  the  decision  to so  terminate  the
Employee's  employment for Cause.  The Employee  shall be given the  opportunity
within 30 calendar  days of the receipt of such notice to meet with the Board to
defend such act or acts,  or failure to act, and the Employee  shall be given 15
days after  such  meeting  to cure such act (or  failure to act) to the  Board's
reasonable satisfaction. Upon failure of the Employee, within such latter 15 day
period, to so cure such act or failure to act, the Employee's  employment by the
Company shall be deemed terminated for Cause. For purposes of this Section 7(a),
any  conduct  engaged  in by the  Employee  shall not be  deemed  to be  willful
misconduct if that conduct is taken,  or engaged in, by the Employee with a good
faith belief that such conduct was in the best interests of the Company.

     (b) Termination  Without Cause. Any Termination of Employment  initiated by
the Company (other than a Termination  for Cause or a Disability  Termination or
due to death) shall be a  "Termination  Without Cause" and the Employee shall be
given at least thirty days prior written notice of any such Termination  Without
Cause.

     8. Termination by the Employee.

     (a) Resignation for Good Reason. Any Termination of Employment initiated by
the Employee  within 90 days  following the  occurrence,  without the Employee's
express written consent,  of any of the following events shall be a "Resignation
for Good  Reason" and the  Company  shall be given at least  fifteen  days prior
written notice of any such Resignation for Good Reason:

(i)      any material reduction in the Employee's responsibilities or  authority
         within the Company, including, without limitation, a material change in
         the Employee's reporting rights or duties or the Employee not being the
         chief executive  officer  of any entity that results from the merger of
         the Company into or with any  other entity  in connection with a Change
         in Control pursuant to Section 11(d) below;

(ii)     any reduction in the Employee's Base Salary or target bonus amount;

(iii)    any  relocation  of  the  Employee's  principal  office  location  to a
         location  more than 35 miles from  Paramus,  New Jersey; and

(iv)     any material  reduction  in  the  Employee's  welfare  benefits  in the
         aggregate  (other   than  any  across-the-board  reduction  imposed  on
         substantially all other members of the Company's senior management).

     (b) Other  Termination  by the  Employee.  Any  Termination  of  Employment
initiated by the Employee (other than a Termination of Employment resulting from
the Employee's death, a Resignation for Good Reason or a Disability Termination)
shall  be a  "Voluntary  Termination"  and the  Company  shall be given at least
thirty days prior written notice of any such Voluntary Termination.

     9. Termination by the Company or by the  Employee--Disability  Termination.
Any Termination of Employment resulting from the Employee's  Disability shall be
a "Disability Termination." For purposes of this Agreement, the term "Employee's
Disability"  shall  mean the  Employee's  illness  or other  physical  or mental
disability  that prevents the Employee from  performing  the  Employee's  duties
hereunder for a period of 90 consecutive days or 120 business days in any twelve
month period. In the event of a Disability  Termination,  the Termination Notice
given to one  party by the other  party  shall  state  that the  Termination  of
Employment is a "Disability Termination."

     10.  Effect  of  Termination  of  Employment  Generally.  In the Event of a
Termination of Employment  (including without limitation a Voluntary Termination
and a Termination for Cause),  neither the Employee nor the Employee's estate or
beneficiaries  shall have any further rights or claims against the Company under
this Agreement  (other than as  contemplated by Section 11), except the right to
receive:

(i)      the portion of the  Base  Salary  which  accrued  with  respect  to the
         period  prior to the  Termination  Date but which remained unpaid as of
         the Termination Date;

(ii)     the aggregate amount of Reimbursable Expenses which were incurred prior
         to the Termination Date but which were not reimbursed by the Company as
         provided in Section 5(d) prior to the Termination Date; and

(iii)    any  other  benefits  to  which  the Employee may be entitled upon such
         Termination of Employment under the plans, programs and policies of the
         Company then in effect, which  benefits  shall be payable in accordance
         with the terms of such plans, programs and policies.

     11.  Effect of  Termination  Without  Cause,  Resignation  for Good Reason,
Disability Termination,  Termination Due to the Employee's Death, or Termination
after a Change in Control  Without  Cause or for Good  Reason.  (a) In the event
that the  Employee's  employment  with the  Company is  terminated  prior to the
occurrence  of a Change in  Control  (as  defined  below)  and such  termination
constitutes  a  Termination  Without  Cause or a  Resignation  for Good  Reason,
neither the Employee nor the Employee's  estate or beneficiaries  shall have any
further rights or claims against the Company under this Agreement other than the
following:

(i)      the right to receive all  amounts  and  benefits to which the  Employee
         would be  entitled  under  Section 10 upon a Termination of Employment;

(ii)     twelve (12) months of Base Salary continuation commencing upon the
         execution by the Employee of a general release in favor of the Company,
         its subsidiaries and affiliates, and its officers, employees, and
         directors, in form and substance acceptable to the Company;

(iii)    twenty-four (24) months additional vesting of the stock options granted
         under and referred to in Section 5(e) above;

(iv)     in the event only of a Termination Without Cause, a pro-rated bonus for
         the year of termination equal to the target bonus amount for such year
         multiplied by a fraction, the numerator of which shall be the number of
         days worked in the current calendar year prior to the Termination
         Without Cause, and the denominator of which shall be 365; and

(v)      continuation of the Employee's (A) life insurance coverage for one year
         after the Termination Date, and (B) medical benefits for one year after
         the Termination Date to be provided through payment of the Employee's
         COBRA premium amount (less any contribution requirement of the Employee
         as of the date of termination), and continuation for one year after the
         Termination Date of any other welfare benefits the Employee was
         participating in on such date to the extent permitted by the terms and
         provisions of the programs providing such benefits.

(b) In the event of a Disability Termination, neither the Employee nor the
Employee's estate or beneficiaries shall have any further rights or claims
against the Company under this Agreement other than the following:

(i)      the right to receive all  amounts  and  benefits to which the  Employee
         would be  entitled  under  Section 10 upon a Termination of Employment;

(ii)     a pro-rated bonus payment, payable upon the execution by the Employee
         of a general release in favor of the Company, its subsidiaries and
         affiliates, and its officers, employees, and directors, in form and
         substance acceptable to the Company for the year of termination equal
         in amount to the average annual bonus amount earned and paid to the
         Employee during the Employment Period multiplied by a fraction, the
         numerator of which is the number of days worked in the current calendar
         year of the Company prior to the Disability Termination, and the
         denominator of which is 365; and

(iii)    twelve (12)months additional vesting of the stock options granted under
         and referred to in Section 5(e) above.

     (c) In the event of the  Employee's  death,  neither the  Employee  nor the
Employee's  estate or  beneficiaries  shall  have any  further  rights or claims
against the Company under this Agreement other than the following:

(i)      the right to receive all  amounts  and  benefits to which the  Employee
         would be  entitled  under  Section 10 upon a Termination of Employment;

(ii)     a pro-rated bonus payment, payable upon the execution by the Employee's
         estate of a general release in favor of the Company, its subsidiaries
         and affiliates, and its officers, employees, and directors, for the
         year of termination equal in amount to the average annual bonus amount
         earned and paid to the Employee during the Employment Period,
         multiplied by a fraction, the numerator of which is the number of days
         worked in the current calendar year of the Company prior to the date of
         the Employee's death, and the denominator of which is 365; and

(iii)    twelve (12)months additional vesting of the stock options granted under
         and referred to in Section 5(e) above.

(d) In the event the Employee's employment with the Company is terminated on or
after the occurrence of a Change in Control and such termination constitutes a
Termination Without Cause or a Resignation for Good Reason, neither the Employee
nor the Employee's estate or beneficiaries shall have any further rights or
claims against the Company under this Agreement other than the following:

(i)       the right to receive all amounts  and  benefits to which the  Employee
          would be  entitled under  Section 10 upon a Termination of Employment;

(ii)     twelve (12) months of Base Salary, payable in one lump sum upon the
         execution by the Employee of a general release in favor of the Company,
         its subsidiaries and affiliates, and its officers, employees, and
         directors, in form and substance acceptable to the Company;

(iii)    100%  accelerated  vesting  and   exercisability  of  all stock options
         outstanding on the date of such  Termination of Employment.

(iv)     in the event only of a Termination Without Cause, a pro-rated bonus for
         the year of termination equal to the target bonus amount for such year
         multiplied by a fraction, the numerator of which shall be the number of
         days worked in the current calendar year of the Company prior to the
         Termination Without Cause, and the denominator of which shall be 365;
         and

(v)      continuation of the Employee's (A) life insurance coverage for one year
         after the Termination Date, and (B) medical benefits for one year after
         the Termination Date to be provided through payment of the Employee's
         COBRA premium amount (less any contribution requirement of the Employee
         as of the date of termination), and continuation for one year after the
         Termination Date of any other welfare benefits the Employee was
         participating in on such date to the extent permitted by the terms and
         provisions of the programs providing such benefits.

     In  addition,  the  Employee's  employment  shall be  deemed  to have  been
terminated  following  a Change in Control  (as  defined  below) by the  Company
without Cause or by the Employee with Good Reason (a) if the Employee reasonably
demonstrates that the Employee's  employment was terminated within 90 days prior
to a Change in Control  without  Cause at the  request  of a person (as  defined
below) who has entered into an agreement  with the Company the  consummation  of
which  will  constitute  a Change  in  Control  (or who has  taken  other  steps
reasonably  calculated  to effect a Change in  Control)  or (b) if the  Employee
terminates  his  employment  for Good Reason within 90 days prior to a Change in
Control and the Employee  reasonably  demonstrates that the  circumstance(s)  or
event(s) which  constitute  such Good Reason occurred at the request of any such
person.

     For  purposes of this  Section  11(d),  "Change in Control"  shall mean and
shall be deemed to have  occurred if (i) any  "person"  (as such term is used in
Sections 13(d) and 14(d) of the Securities Exchange Act of 1934, as amended (the
"Exchange Act")) is or becomes the "beneficial  owner" (as defined in Rule 13d-3
under the Exchange Act),  directly or  indirectly,  of securities of the Company
representing  50% or more of the  combined  voting power of the  Company's  then
outstanding  securities;  or (ii)  during any period of two  consecutive  years,
individuals  who at the  beginning  of  such  period  constitute  the  Board  of
Directors of the Company  cease for any reason to constitute at least a majority
thereof  unless the election,  or the  nomination  for election by the Company's
stockholders, of each new director was approved by a vote of at least a majority
of the  directors of the Company then still in office who were  directors at the
beginning of the period. If the benefits payable hereunder,  together with other
payments in the nature of compensation to or with respect to the Employee, would
otherwise  be subject to the excise  taxes  imposed  under  Section  280G of the
Internal Revenue Code of 1986, as amended ("Code"), and if the net value of such
benefits and payments in the nature of  compensation,  after  reduction for such
taxes,  is less than the  aggregate  value of the  benefits  and payments in the
nature of compensation  determined as if such amounts had been $1.00 less than a
maximum amount which could be paid without  imposition of excise taxes, then the
benefits  payable  hereunder  shall be reduced to highest  amount such that such
excise  taxes  shall not be imposed  with  respect to the  benefits or the other
payments in the nature of compensation. It is the intention of this provision to
reduce  benefits  payable  hereunder only if the Employee would be in a superior
position  taking into account such excise taxes than if such payments were made,
and such reduction  shall,  in any event,  be the least amount in order that the
Employee  be better off with the  reduction  than  before  such  reduction.  The
calculation of the value of benefits payable hereunder and other payments in the
nature of compensation,  and the implications of the excise tax rules of Section
280G of the Code,  shall be  determined  by the  Company in good faith  based on
written advice of a national accounting firm.

     12. Non-solicitation of Employees. The Employee agrees that during the term
of the Employee's employment with the Company and for a period of one year after
the  termination of the Employee's  employment  with the Company for any reason,
the Employee  shall not  directly or  indirectly  recruit,  solicit or otherwise
induce or attempt to induce any current employees,  or employees  separated from
employment  with the Company for less than one year,  of, or any  consultants or
scientific  or other  advisors  to, the Company to leave the  employment  of the
Company or to cease advising or providing services to the Company.

     13.  Non-competition.  The  Employee  agrees  that  during  the term of the
Employee's  employment  with the  Company and for a period of one year after the
termination of the Employee's  employment with the Company for any reason (other
than  a  Termination   Without  Cause),  the  Employee  shall  not  directly  or
indirectly,  except  as a  passive  investor  in  publicly  held  companies  not
exceeding 3% of the issued and outstanding  shares of any such company,  engage,
within or with respect to the United States of America,  in competition with the
Company or any of its subsidiaries, or own or control any interest in, or act as
director,  officer or employee of, or consultant  to, any firm,  corporation  or
institution  directly or indirectly  engaged in competition  with the Company or
any of its subsidiaries.  For purposes of this Section 13, "competition with the
Company or any or its  subsidiaries"  shall mean engaging in or assisting others
in the discovery or  development of products or services which have been, or are
being,  developed by the Company (or are substantially  related to such products
or  services)  as of or at the  Termination  Date  and/or  activities  otherwise
involving  the  Company's  technology  platform  at the  Termination  Date,  and
"products" shall be defined and identified,  among other criteria,  by reference
to the underlying mechanisms of action (e.g., their biological targets).

     14. Confidentiality. The Employee agrees that the Employee will not (except
as required in the course of employment with the Company),  both during the term
of Employee's employment with the Company and thereafter, communicate or divulge
to, or use for Employee's  own benefit or the benefit of any other person,  firm
or organization, any confidential and proprietary information of the Company and
its subsidiaries (other than when required to do so in good faith to perform the
Employee's duties and responsibilities under this Agreement or when (a) required
to  do  so  by a  lawful  order  of  a  court  of  competent  jurisdiction,  any
governmental  authority  or agency,  or any  recognized  subpoena  power).  All,
records, files, memoranda,  reports, price lists, drawings,  plans, sketches and
documents and the like, relating to the business of the Company,  which Employee
shall use or prepare or come into  contact  within the course of, in  connection
with, or as a result of employment with the Company,  shall remain the Company's
sole  and  exclusive  property.   Notwithstanding   the  immediately   preceding
sentences,  Confidential  Information shall not include any information that is,
or becomes,  generally  available to the public (unless such availability occurs
as a result of the Employee's breach of any portion of this Section 14.

     15.  Ownership  of  Inventions.  Each  Invention  made,  conceived or first
actually  reduced to practice by the  Employee,  whether  alone or jointly  with
others,  during the term of  Employee's  employment  with the  Company  and each
Invention made, conceived or first actually reduced to practice by the Employee,
whether alone or jointly with others,  within one year after the  termination of
Employee's  employment  with  the  Company  which  relates  in any  way to  work
performed  for the Company  during the term of Employee's  employment,  shall be
promptly  disclosed in writing to the Board.  Such report shall be  sufficiently
complete in technical detail and appropriately  illustrated by sketch or diagram
to convey to one  skilled in the art of which the  invention  pertains,  a clear
understanding of the nature, purpose,  operations, and, to the extent known, the
physical,  chemical,  biological or other  characteristics of the Invention.  As
used in this Agreement, "Invention" means any invention, discovery or innovation
with  regard  to  chemistry,  enzymology,  biotechnology,  genetic  engineering,
medicine,   pharmaceuticals  or  recombinant  DNA  technology,  whether  or  not
patentable,  made, conceived, or first actually reduced to practice by Employee,
alone or jointly  with others,  in the course of, in  connection  with,  or as a
result of service as an  executive of the Company,  including  any art,  method,
process,  machine,  manufacture,   design  or  composition  of  matter,  or  any
improvement  thereof, or any variety of plant or microorganism.  Each invention,
as herein defined,  shall be the sole and exclusive property of the Company. The
Employee  agrees to execute an  assignment  to the Company or its nominee of the
Employee's  entire right,  title and interest in and to any  Invention,  without
compensation  beyond  that  provided in this  Agreement.  The  Employee  further
agrees,  upon the request of the Company and at its  expense,  that the Employee
will  execute any other  instrument  and  document  necessary  or  desirable  in
applying  for and  obtaining  patents  in the United  States and in any  foreign
country with respect to any Invention.  The Employee further agrees,  whether or
not the Employee is then an employee of the Company,  to cooperate to the extent
and in the manner  reasonably  requested  by the Company in the  prosecution  or
defense of any claim involving a patent covering any Invention or any litigation
or other claim or proceeding  involving any Invention covered by this Agreement,
but all expenses thereof shall be paid by the Company.

     16. Breach of Restrictive Covenants.

     (a) The  Employee  acknowledges  and agrees that the  Company  will have no
adequate  remedy  at law,  and  would be  irreparably  harmed,  if the  Employee
breaches or  threatens  to breach any of the  provisions  of Sections 12, 13, 14
and/or 15 of this  Agreement.  The  Employee  agrees that the  Company  shall be
entitled  to  equitable  and/or  injunctive  relief  to  prevent  any  breach or
threatened breach of such Sections,  and to specific  performance of each of the
terms of such Sections in addition to any other legal or equitable remedies that
the Company may have.  The Employee  further agrees that the Employee shall not,
in any equity  proceeding  relating to the  enforcement of the terms of Sections
12, 13, 14 and/or 15, raise the defense that the Company has an adequate  remedy
at law.

     (b) The terms and  provisions of Sections 12, 13, 14 and/or 15 are intended
to be separate and divisible  provisions and if, for any reason, any one or more
of them is held to be invalid or  unenforceable,  neither  the  validity  or the
enforceability  of any  other  provision  of this  Agreement  shall  thereby  be
affected.  It is the  intention  of the  parties  to  this  Agreement  that  the
potential restrictions on the Employee's future employment imposed by Section 13
be reasonable in both duration and geographic  scope and in all other  respects.
If for any reason any court of competent  jurisdiction shall find any provisions
of Section 13  unreasonable  in duration or geographic  scope or otherwise,  the
Employee and the Company agree that the restrictions and prohibitions  contained
herein shall be effective to the fullest extent allowed under  applicable law in
such jurisdiction.

     17.  Notices.  All  notices or other  communications  that are  required or
permitted  hereunder  shall be in writing and shall be deemed to have been given
if  (a)   personally   delivered   or   sent   by   telecopier,   (b)   sent  by
nationally-recognized  overnight courier or (c) sent by certified mail,  postage
prepaid, return receipt requested, addressed as follows:

                  if to the Employee, at:

                           Mr. Errol de Souza
                           c/o Synaptic Pharmaceutical Corporation
                           215 College Road
                           Paramus, New Jersey  07652

                  with a copy to:

                           Claude E. Johnston
                           Managing Partner
                           Pearl Meyer & Partners
                           445 Park Avenue
                           New York, NY  10022-2606

                  if to the Company, at:

                           Synaptic Pharmaceutical Corporation
                           215 College Road
                           Paramus, New Jersey 07652
                           Attention: Chairman of the Compensation Committee

                           with a copy to:

                           Stephen W. Skonieczny, Esq.
                           Dechert
                           30 Rockefeller Plaza
                           New York, NY  10112

     or to such  other  address  as the party to whom  notice is to be given may
have furnished to each other party in writing in accordance  herewith.  Any such
communication  shall be deemed to have been  received  when  delivered.  As used
herein, the term "Business Day" means a day that is not a Saturday,  a Sunday or
a day on  which  banking  institutions  in the  city  to  which  the  notice  or
communication is to be sent are not required to be open.

     18.  Entire  Agreement;  Amendments.  This  Agreement  contains  the entire
agreement  between the parties  hereto with respect to the subject matter hereof
and  supersedes  all  prior  or  contemporaneous  negotiations,  correspondence,
understandings  and agreements  between the parties with respect  thereto.  This
Agreement may be amended only by an agreement in writing  signed by both parties
hereto.  Anything  contained  herein  to  the  contrary   notwithstanding,   the
provisions of this Agreement  shall survive the expiration or early  termination
of the Employment Period.

     19.  Assignment.  This  Agreement  is personal in its nature.  Accordingly,
Employee shall not assign this Agreement or any rights or obligations  hereunder
to any other person or entity.

     20.  Benefits of  Agreement.  The  provisions  of this  Agreement  shall be
binding upon and inure to the benefit of the heirs, beneficiaries, executors and
administrators of the Employee and the successors and assigns of the Company.

     21. Obligation of the Company's  Successors.  The Company shall require any
successor to all or  substantially  all of its business  and/or assets,  whether
direct or indirect, by purchase, merger, consolidation, acquisition of stock, or
otherwise,  by an agreement  inform and substance  satisfactory to the Employee,
expressly to assume and agree to perform  this  Agreement in the same manner and
to the same  extent as the  Company  would be  required  to  perform  if no such
succession had taken place.

     22.  Waiver of  Breach.  A waiver of any  breach of any  provision  of this
Agreement  shall not  constitute  or operate as a waiver of any other  breach of
such  provision  or of any other  provision,  and any  failure  to  enforce  any
provision hereof shall not operate as a waiver of such provision or of any other
provision.

     23.  Execution in  Counterparts.  This  Agreement may be executed in one or
more counterparts,  each of which shall be deemed an original,  but all of which
shall constitute one and the same instrument.

     24.  Headings.   The  headings  of  sections  in  this  Agreement  are  for
convenience  only,  are not a part of this  Agreement  and shall not  affect the
construction of the provisions of this Agreement.

     25.  Governing Law. This Agreement  shall be governed by, and construed and
enforced in accordance  with, the laws of the State of New Jersey without giving
effect to principles of conflicts of laws.

     26.  Enforceability.  In the event that any provision of this  Agreement is
determined to be partially or wholly invalid,  illegal or  unenforceable  in any
jurisdiction,  then such pro vision shall, as to such jurisdiction,  be modified
or restricted to the extent necessary to make such provision valid,  binding and
enforceable,  or, if such provision cannot be modified or restricted,  then such
provision  shall,  as to such  jurisdiction,  be deemed to be excised  from this
Agreement;  provided, however, that the binding effect and enforceability of the
remaining provisions of this Agreement, to the extent that the economic benefits
conferred  upon the  parties by virtue of this  Agreement  remain  substantially
unimpaired,  shall not be affected or impaired in any manner,  and that any such
invalidity, illegality or unenforceability with respect to such provisions shall
not invalidate or render unenforceable such provision in any other jurisdiction.

     27. Withholding. The Company may withhold from any payments or benefits due
or payable  under this  Agreement or otherwise  such taxes and other  amounts as
shall be required to be withheld  pursuant to any applicable law,  regulation or
rule.

     28. Arbitration. (a) The parties hereto agree that any dispute, controversy
or claim  arising out of,  relating  to, or in  connection  with this  Agreement
(including,   without  limitation,   any  claim  regarding  or  related  to  the
interpretation,  scope, effect,  enforcement,  termination,  extension,  breach,
legality,  remedies  and other  aspects of this  Agreement  or the  conduct  and
communications of the parties regarding this Agreement and the subject matter of
this  Agreement)  shall be settled by  arbitration  at the  offices of  Judicial
Arbitration and Mediation Services,  Inc. or successor  organization for binding
arbitration  in New York City by a single  arbitrator.  The arbitrator may grant
injunctions  or other relief in such dispute or  controversy.  All awards of the
arbitrator shall be binding and  non-appealable.  Judgment upon the award of the
arbitrator may be entered in any court having jurisdiction. The arbitrator shall
apply New Jersey law to the merits of any dispute or claims,  without  reference
to any rules of  conflicts of law that might  result in the  application  of any
other  state's law.  Suits to compel or enjoin  arbitration  or to determine the
applicability  or legality of arbitration  shall be brought in the United States
District  Court for the  Southern  District of New York,  or if that court lacks
jurisdiction, in a state court located within the geographic boundaries thereof.
Notwithstanding  the foregoing,  no party to this  Agreement  shall be precluded
from applying to a proper court for injunctive  relief by reason of the presence
of this Section 28 or the prior or  subsequent  commencement  of an  arbitration
proceeding as herein provided.

     (b) The Employee has read and  understands  this Section 28 which discusses
arbitration.  The  Employee  understands  that by signing  this  Agreement,  the
Employee  agrees  to  submit  any  claims  arising  out of  relating  to,  or in
connection with this Agreement, or the interpretation,  validity,  construction,
performance, breach or termination thereof, or his employment or the termination
thereof, to binding arbitration, and that this arbitration provision constitutes
a waiver of the  Employee's  right to a jury trial and relates to the resolution
of all disputes relating to all aspects of the  employer/employee  relationship,
including but not limited to the following:

(i)      Any and all claims for wrongful discharge of employment, breach of
         contract, both express and implied; breach of the covenant of good
         faith and fair dealing, both express and implied; negligent or
         intentional infliction of emotional distress; negligent or intentional
         misrepresentation; negligent or intentional interference with contract
         or prospective economic advantage; and defamation;

(ii)     Any and all claims for violation of any federal, state or municipal
         statute, including, without limitation, Title VII of the Civil Rights
         Act of 1964, as amended the Civil Rights Act of 1991, the Equal Pay
         Act, the Employee Retirement Income Security Act, as amended, the Age
         Discrimination in Employment Act of 1964, the Americans wit
         Disabilities Act of 1990, the Family and Medical Leave Act of 1993, and
         the Fair Labor Standards Act; and

(iii)    Any and all claims arising out of any other federal, state or local
         laws or regulations relating to employment or employment
         discrimination.

     29. Legal Fees and Other Expenses. In the event that a claim for payment or
benefits under this Agreement is disputed,  the Employee shall be reimbursed for
all  attorney  fees and  expenses  incurred by the  Employee in pursing any such
claim,  provided  that the  Employee  substantially  prevails  in respect of the
disputed claim by reason of litigation,  arbitration or settlement. In addition,
the  Employee  shall be paid or  reimbursed  for all  reasonable  legal fees and
expenses incurred by the Employee in connection with the review, preparation and
negotiation of this Agreement.

<PAGE>

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

                                 SYNAPTIC PHARMACEUTICAL CORPORATION

                                 By:/s/ Jonathan Leff
                                    -------------------------------------
                                 Name:
                                 Title:    Member of the Compensation Committee

                                  /s/ Errol de Souza
                                  ---------------------------------------
                                      Errol de SouzaISO Plan Option

                                 NONTRANSFERABLE
                        INCENTIVE STOCK OPTION AGREEMENT

                                       for

                                 Errol de Souza
                      -----------------------------------

     THIS AGREEMENT (this "Agreement"), dated as of September 9, 2002, is by and
between  SYNAPTIC  PHARMACEUTICAL   CORPORATION,  a  Delaware  corporation  (the
"Company"),  and Errol de Souza (the "Optionee," which term as used herein shall
be deemed to include  any  successor  to the  Optionee by will or by the laws of
descent and distribution, unless the context shall otherwise require).

                              W I T N E S S E T H:

     WHEREAS,  the  Company  and  the  Optionee  are  parties  to an  Employment
Agreement dated as of September 9, 2002 (the "Employment Agreement");

     WHEREAS,  the Employment  Agreement  provides for the grant of an option to
acquire 250,000 shares (the "Plan Option Shares") of the Company's  common stock
pursuant to the Synaptic  Pharmaceutical  Corporation  1996  Incentive Plan (the
"Plan"),  with such option to be treated as an  "incentive  stock option" to the
maximum extent permitted by law;

     WHEREAS,  based on the closing sale price of the Company's  common stock on
the Start Date (as defined below), no more than 69,565 of the Plan Option Shares
may be  subject  to an  incentive  stock  option  agreement  and this  agreement
provides an option for that number of shares;

     WHEREAS,  a separate  nonqualified  option  agreement is being entered into
between the Company and the Optionee to provide an option for the balance of the
Plan Option Shares; and

     WHEREAS, pursuant to the Plan, the Company, acting through the Compensation
Committee (the  "Committee") of its Board of Directors (the "Board"),  effective
September  9, 2002 (the  "Start  Date"),  granted to the  Optionee  an option to
purchase up to an aggregate of 69,565 shares of Common  Stock,  $0.01 par value,
of the  Company  (the  "Common  Stock"),  at the price of $5.75 per share,  such
option to be for the term and upon the terms and conditions hereinafter stated.

     NOW,  THEREFORE,  in  consideration of the mutual premises and undertakings
hereinafter set forth, the parties hereto agree as follows:

     1. Option;  Option  Price.  Pursuant to said action of the  Committee,  the
Company has granted to the Optionee the option (the "Option") to purchase,  upon
and  subject to the terms and  conditions  of this  Agreement  and the terms and
conditions  of the Plan (which are hereby  incorporated  by  reference  herein),
69,565 shares (the "Option  Shares") of Common Stock of the Company at the price
of $5.75 per share (the "Option Price"), which Option is intended to qualify for
Federal income tax purposes as an "incentive stock option" within the meaning of
Section 422 of the Internal Revenue Code of 1986, as amended (the "Code").

     2. Term.  The term (the "Option  Term") of the Option shall commence on the
Start Date and expire on the tenth  anniversary  of the Start  Date,  unless the
Option shall  theretofore  have been  terminated  in  accordance  with the terms
hereof or of the Plan.

     3. Exercisability; Time of Exercise.

     (a) General.  Unless  accelerated  in the discretion of the Committee or as
otherwise  provided herein,  the Option shall vest and become  exercisable as to
1/48th of the Option Shares each month,  commencing on the one-month anniversary
of the Start Date, so that the Option shall be vested and  exercisable as to all
of the Option Shares on the 48-month  anniversary  of the Start Date. The Option
shall  remain  exercisable  as to all shares as to which is  becomes  vested and
exercisable  until the  expiration  of the Option Term,  unless it is terminated
earlier as provided in any of the other  paragraphs of this Section 3 or Section
6 or as provided in the Plan.

     (b) Termination for Cause. If the Optionee shall cease to be an employee of
the  Company  as the  result  of a  Termination  for Cause  (as  defined  in the
Employment  Agreement),  the Option shall  automatically  terminate  on, and the
Optionee  shall have no further  right to exercise  the Option on or after,  the
date as of which  notice of such  termination  is given to the  Optionee  by the
Company.  As used in this  Agreement,  the term "Cause" has the meaning given to
such term in the Employment Agreement.

     (c)  Termination  Without  Cause;  Resignation  for  Good  Reason.  If  the
Optionee's   employment  with  the  Company   terminates  and  such  termination
constitutes a Termination Without Cause (as defined in the Employment Agreement)
or a Resignation for Good Reason (as defined in the Employment  Agreement),  the
vesting  of the  Option  shall  accelerate  so  that,  as of the  date  of  such
termination,  the Option shall be exercisable for the Option Shares, if any, for
which it has become  exercisable  pursuant to paragraph (a) of this Section 3 as
of the date of such termination plus an additional 24/48ths of the Option Shares
(up to the  total  number  of  Option  Shares).  The  Option  shall in any event
terminate  upon,  and the Optionee  shall have no further  right to exercise the
Option after,  the earlier of (i) the  expiration of the Option Term and (ii) 30
days after the date of such a termination.

     (d) Voluntary  Termination.  If the Optionee terminates his employment with
the Company by a Voluntary Termination (as defined in the Employment Agreement),
the Option shall be exercisable for the Option Shares,  if any, for which it has
become  exercisable  pursuant to paragraph  (a) of this Section 3 as of the date
the  Optionee  gives notice of such  termination.  The Option shall in any event
terminate  upon and the  Optionee  shall have no further  right to exercise  the
Option after,  the earlier of (i) the  expiration of the Option Term and (ii) 30
days after the date the Optionee gives notice of such termination.

     (e) Disability  Termination.  If the Optionee's employment with the Company
terminates and such termination constitutes a Disability Termination (as defined
in the  Employment  Agreement),  the vesting of the Option shall  accelerate  so
that, as of the date of such  termination,  the Option shall be exercisable  for
the Option  Shares,  if any,  for which it has become  exercisable  pursuant  to
paragraph  (a) of this  Section  3 as of the  date of such  termination  plus an
additional  12/48ths  of the  Option  Shares  (up to the total  number of Option
Shares).  The Option shall in any event  terminate  upon, and the Optionee shall
have no further  right to  exercise  the Option  after,  the  earlier of (i) the
expiration  of the  Option  Term  and (ii)  180  days  after  the date of such a
termination;  provided, however, that, in the case of any such termination other
than a  termination  resulting  from the Optionee  being  "disabled"  within the
meaning of Section  22(e)(3) of the Code,  the Option shall no longer be treated
as an  "incentive  stock  option"  within the meaning of Section 422 of the Code
unless exercised within three (3) months following the date of such termination.
For purposes of Agreement,  the term  "Disability"  has the meaning given to the
term "Employee's Disability" in the Employment Agreement.

     (f) Termination as a Result of Death. If the Optionee's employment with the
Company  terminates as a result of the Optionee's death, the Option shall, as of
the  date of such  termination,  be  exercisable  by the  Optionee's  Designated
Beneficiary  (as  defined  in the Plan) or  personal  representatives,  heirs or
legatees  (as  provided  in the  Plan),  and the  vesting  of the  Option  shall
accelerate  so that,  as of the date of such  termination,  the Option  shall be
exercisable for the Option Shares,  if any, for which it has become  exercisable
pursuant to paragraph  (a) of this Section 3 as of the date of such  termination
plus an  additional  12/48ths  of the Option  Shares (up to the total  number of
Option  Shares).  The Option shall in any event terminate upon, and the Optionee
(and the  Designated  Beneficiary)  shall have no further  right to exercise the
Option after,  the earlier of (i) the expiration of the Option Term and (ii) one
year after the date of death.  Notwithstanding anything contained in the Plan to
the contrary,  the Option shall  continue to be treated as an  "incentive  stock
option"  within  the  meaning  of  Section  422 of the  Code  even  if it is not
exercised  until  after the third  month  following  the date of the  Optionee's
death.

     (g) Death Following Disability. In the event of the Optionee's death within
180 days  following  a  Disability  Termination  (as  defined in the  Employment
Agreement),  the  Option  shall  thereafter  be  exercisable  by the  Optionee's
Designated  Beneficiary or personal  representatives,  heirs or legatees, to the
extent,  if any, which it shall have vested and become  exercisable  pursuant to
paragraphs  (a) and (d) of this Section 3 for a period of one (1) year following
the date of death but in no event later than the  expiration of the Option Term;
provided,  however,  that, in the case in which the  Optionee's  termination  of
employment  resulted from the Optionee  being  "disabled"  within the meaning of
Section  22(e)(3)  of the Code,  the  Option  shall no longer be  treated  as an
"incentive  stock  option"  within the meaning of Section 422 of the Code unless
exercised  within  one (1)  year  following  the date of such  termination;  and
provided further,  however, that, in all other cases, the Option shall no longer
be treated as an "incentive  stock option"  within the meaning of Section 422 of
the Code unless  exercised  within three (3) months  following  the date of such
termination.

     4.  Procedure for Exercise.  (a) The Option may be exercised,  from time to
time,  in whole or in part  (but for the  purchase  of whole  shares  only),  by
delivery of a written  notice (the  "Notice") from the Optionee to the Secretary
of the Company, which Notice shall:

     (i) state  that the  Optionee  elects to  exercise  the  Option  under this
Agreement;

     (ii)  state the number of shares  with  respect  to which the  Optionee  is
exercising the Option (the "Acquired Shares");

     (iii) include any  representations  of the Optionee  required under Section
7(b) hereof;

     (iv)  state the method of  payment  for the  Acquired  Shares  pursuant  to
Section 4(b);

     (v) in the event that the Option  shall be  exercised  by any person  other
than the Optionee pursuant to Sections 3 and 8, include appropriate proof of the
right of such person to exercise the Option; and

     (vi)  state the date upon which the  Optionee  desires  to  consummate  the
purchase of the Acquired  Shares (which date must be prior to the termination of
such Option).

     (b)  Payment of the Option  Price for the  Acquired  Shares  shall,  unless
otherwise  provided  by the  Committee,  be made (i) in cash or by  personal  or
certified  check,  or (ii) by delivery of shares of the  Company's  Common Stock
owned by the  Optionee  for more than six months  prior to the date of  exercise
having a value equal to the aggregate Option Price of the Acquired Shares,  with
such  delivered  shares to be valued at the closing sale price of the  Company's
Common  Stock on the Nasdaq  National  Market on the date of exercise  (provided
that, if the Company's Common Stock does not trade on the Nasdaq National Market
at such time, the value thereof shall be determined by the Committee in a manner
it deems appropriate).

     5. No Rights as a  Stockholder.  The Optionee shall not have any privileges
of a  stockholder  with  respect to any Option  Shares until the date of a stock
certificate representing such Option Shares is issued to the Optionee.

     6. Adjustments.

     (a) Stock Dividends,  Splits, Subdivisions or Combinations.  Subject to the
other  provisions  of this  Section  6, if,  at any time  while  the  Option  is
outstanding,  the  Common  Stock is changed  by reason of  dividends  payable in
Common Stock or splits,  subdivisions or combinations of shares of Common Stock,
then the  number  of  shares  of  Common  Stock  deliverable  upon the  exercise
thereafter of the Option shall be increased or decreased proportionately, as the
case may be, without change in the aggregate Option Price.

     (b) Cash Mergers.  Upon the occurrence of a merger on  consolidation of the
Company with another  corporation in a transaction in which the  stockholders of
the Company receive cash  consideration  in exchange for their shares of capital
stock  of  the  Company  (a  "cash  merger"),  the  Option  shall  automatically
terminate;  provided,  however,  that the  Optionee  shall be given (i)  written
notice of such cash merger at least 20 days prior to its proposed effective date
(as  specified  in such  notice)  and (ii) an  opportunity,  during  the  period
commencing  with  delivery of such notice and ending ten (10) days prior to such
proposed  effective date, to exercise the Option in full as to all of the Option
Shares, whether or not then vested.

     (c)  Assumption  or  Substitution  of  Options.   Notwithstanding  anything
contained  herein  or in the Plan to the  contrary,  Section  6(b)  shall not be
applicable if provision  shall be made in  connection  with such cash merger for
the  assumption  of the Option by, or the  substitution  for the Option of a new
option   covering  the  stock  of,  the   surviving,   successor  or  purchasing
corporation,  or a parent or subsidiary thereof, with appropriate adjustments as
to the number, kind and option price of shares subject to such option; provided,
however,  that the Board  shall,  to the extent not  inconsistent  with the best
interests  of the  Company  or  its  subsidiaries  (such  best  interests  to be
determined  in good faith by the Board,  in its sole  discretion),  use its best
efforts to ensure that any such assumption or substitution will not constitute a
modification,  extension or renewal of the Option  within the meaning of Section
424(h) of the Code and the regulations thereunder.

     (d) Corporate Transactions. Notwithstanding anything contained herein or in
the Plan to the contrary,  upon the occurrence of (i) a merger or  consolidation
of the Company  with another  corporation  in a  transaction  (other than a cash
merger) in which the  Company  shall not  survive or in which the Company is the
survivor but its capital stock is exchanged for stock,  securities,  or property
of another  entity or (ii) a sale of all or  substantially  all of the assets of
the Company (any  transaction  described in clause (i) or (ii) being referred to
herein as a "corporate transaction"), provision shall be made in connection with
such  corporate  transaction  for  the  assumption  of  the  Option  by,  or the
substitution  for  the  Option  of a new  option  covering  the  stock  of,  the
surviving,  successor  or  purchasing  corporation,  or a parent  or  subsidiary
thereof, with appropriate adjustments as to the number, kind and option price of
shares subject to such option;  provided,  however, that the Board shall, to the
extent  not  inconsistent  with  the  best  interests  of  the  Company  or  its
subsidiaries  (such best  interests to be determined in good faith by the Board,
in its sole discretion), use its best efforts to ensure that any such assumption
or substitution will not constitute a modification,  extension or renewal of the
Option  within the  meaning of  Section  424(h) of the Code and the  regulations
thereunder.

     (e)  Termination  Following a Change of Control.  Notwithstanding  anything
contained  herein or in the Plan to the  contrary,  in the event the  Optionee's
employment  with the Company or the person which is the surviving,  successor or
purchasing  corporation,  is  terminated  at any time  following  any  Change of
Control  (as  defined  in  the  Employment   Agreement)  and  such   termination
constitutes a Termination Without Cause (as defined in the Employment Agreement)
or a Resignation for Good Reason (as defined in the Employment  Agreement),  the
Option shall become exercisable in full as to all Option Shares,  whether or not
vested,  as of the date of such  termination,  and the  Optionee  shall have the
right to exercise  the Option as to any or all of such shares  until the earlier
of (i) the  expiration  of the Option Term and (ii) the 90th day  following  the
date of such termination, at which time the Option shall terminate.

     7.  Additional  Provisions  Related to  Exercise.  (a) The Option  shall be
exercisable  only on such  date or dates and  during  such  period  and for such
number of shares of Common Stock as are set forth in this Agreement.

     (b) To exercise the Option,  the Optionee  shall follow the  procedures set
forth in Section 4 hereof.  Upon the exercise of the Option as a time when there
is not in effect a registration  statement  under the Securities Act of 1933, as
amended,  relating to the shares of Common Stock  issuable  upon exercise of the
Option,  the Optionee  shall provide the Company with such  representations  and
warranties  as may be required by the  Committee to the effect that the Acquired
Shares are being acquired for investment and not with a view to the distribution
thereof. Anything contained herein to the contrary notwithstanding, in the event
the Board  shall  determine,  in its sole and  subjective  discretion,  that the
registration,  qualification  or listing of the Option  Shares upon a securities
exchange  or under any state or Federal  law,  or the consent or approval or any
government or regulatory body, is necessary or desirable as a condition of or in
connection with the exercise of the Option, the Option may not be exercised,  in
whole or in part, unless and until such  registration,  qualification,  listing,
consent or approval  shall have been effected or obtained free of any conditions
not acceptable to the Board.

     (c) The Option shall not be affected by any change of duties or position of
the  Optionee  (including  transfer  to or  from a  subsidiary),  so long as the
Optionee  continues to be an employee of the Company or one of its subsidiaries.
Nothing in the Option granted hereunder shall confer upon the Optionee any right
to continue in the employ of the Company or any of its subsidiaries or interfere
in any way with the right of the Company or its subsidiaries or the stockholders
of the Company, as the case may be, to terminate the Optionee's employment or to
increase or decrease the Optionee's compensation at any time.

     8.  Restriction on Transfer.  The Option may not be  transferred,  pledged,
assigned,  hypothecated  (whether by  operation  of law or  otherwise),  sold or
otherwise disposed of in any way by the Optionee,  except by will or by the laws
of descent and  distribution,  and may be  exercised  during the lifetime of the
Optionee only by the Optionee. If the Optionee dies, the Option shall thereafter
be  exercisable,  during the  applicable  period  specified in Section 3, by the
Optionee's Designated Beneficiary or personal representatives, heirs or legatees
(as provided in the Plan) to the full extent to which the Option was exercisable
by the  Optionee at the time of the  Optionee's  death as provided  herein.  The
Option shall not be subject to  execution,  attachment or similar  process.  Any
attempted transfer, pledge, assignment, hypothecation, sale or other disposition
of the Option contrary to the provisions  hereof, and the levy of any execution,
attachment  or  similar  process  upon  the  Option,  shall be null and void and
without effect.

     9.  Restrictive  Legends.  In  order to  reflect  certain  restrictions  on
disposition of the shares acquired upon exercise of the Option (the  "Restricted
Shares"), all stock certificates representing the Restricted Shares issued shall
have affixed thereto any legends determined by the Company to be appropriate.

     10.  Notices.  All notices or other  communications  which are  required or
permitted  hereunder  shall  be in  writing  and  sufficient  if (i)  personally
delivered or sent by telecopier,  (ii) sent by  nationally-recognized  overnight
courier or (iii) sent by registered or certified mail,  postage prepaid,  return
receipt requested, addressed as follows:

                  if to the Optionee, to:

                           Errol de Souza
                           c/o Synaptic Pharmaceutical Corporation
                           215 College Road
                           Paramus, New Jersey 07652

                  with a copy to:

                           Claude E. Johnston
                           Managing Partner
                           Pearl Meyer & Partners
                           445 Park Avenue
                           New York, NY 10022-2606

                  if to the Corporation, to:

                           Synaptic Pharmaceutical Corporation
                           215 College Road
                           Paramus, New Jersey 07652
                           Attention: President Telecopier: 201-261-0623

                  With a copy to:

                           Robert Murray, Esq.
                           Baker Botts L.L.P.
                           30 Rockefeller Plaza
                           New York, NY 10112

                           Stephen W. Skonieczny, Esq.
                           Dechert
                           30 Rockefeller Plaza
                           New York, NY 10112

     or to such  other  address  as the party to whom  notice is to be given may
have furnished to each other party in writing in accordance  herewith.  Any such
communication  shall  be  deemed  to have  been  given  (i) when  delivered,  if
personally  delivered,  sent by  telecopier  or  sent  by  nationally-recognized
overnight  courier and (ii) on the third Business Day (as  hereinafter  defined)
following the date on which the piece of mail containing such  communication  is
posted, if sent by mail. As used herein,  "Business Day" means a day that is not
a Saturday,  Sunday or a day on which banking  institutions in the city to which
the notice or communication is to be sent are not required to be open.

     11.  Disqualifying  Disposition.  If the Optionee disposes of any shares of
Common Stock acquired upon the exercise of the Option within two years after the
Start Date or within one year after such  shares were  acquired  pursuant to the
exercise of the Option, the Optionee shall notify the Company in writing of such
disposition. Any notice required under this Section shall be given within thirty
days of such disposition.

     12. No Waiver. No waiver of any breach or condition of this Agreement shall
be deemed to be a waiver of any other or subsequent breach or condition, whether
of like or different nature.

     13.  Optionee  Undertaking.  The Optionee  hereby  agrees to take  whatever
additional actions and execute whatever additional  documents the Company may in
its  reasonable  judgement  deem necessary or advisable in order to carry out or
effect one or more of the  obligations or  restrictions  imposed on the Optionee
pursuant to the express provisions of this Agreement.

     14.  Modification  of Rights.  The rights of the  Optionee  are  subject to
modification and termination in certain events as provided in this Agreement and
the Plan.

     15.  Governing Law. This  Agreement  shall be governed by, and construed in
accordance  with,  the laws of the State of New Jersey  without giving effect to
principles of conflicts of laws.

     16.   Counterparts.   This  Agreement  may  be  executed  in  one  or  more
counterparts,  each of which shall be deemed to be an original, but all of which
together shall constitute one and the same instrument.

     17.  Entire  Agreement.  This  Agreement,  the  Employment  Agreement  (the
provisions of which related to stock options are hereby  incorporated  herein by
reference) and the Plan constitute the entire agreement between the parties with
respect to the subject  matter hereof and thereof,  and supersede all previously
written or oral negotiations,  commitments,  representations and agreements with
respect  thereto.  In the event of any  inconsistency  between the terms of this
Agreement and the terms of the Plan, the terms of the Plan shall control.

                            [Signature Page Follows]

<PAGE>

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

                                     SYNAPTIC PHARMACEUTICAL CORPORATION

                                     By:/s/ Jonathan Leff
                                        ---------------------------------
                                     Name:
                                     Title:

                                     OPTIONEE

                                     /s/ Errol B. De Souza
                                     ------------------------------------
                                         Errol de Souza

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