ADDENDUM
                                       TO
                             STOCK OPTION AGREEMENT


                  The following provisions are hereby incorporated into, and are
hereby  made  a  part  of,   that   certain   Stock   Option   Agreement   dated
_________________   (the   "Option   Agreement")   by   and   between   Atlantic
Pharmaceuticals,  Inc. (the "Corporation") and  __________________  ("Optionee")
evidencing the non-statutory stock option granted on such date to Optionee under
the terms of the Corporation's 1995 Stock Option Plan, and such provisions shall
be effective immediately.  Capitalized terms in this Addendum, to the extent not
otherwise defined herein,  shall have the meanings assigned to such terms in the
Option Agreement.

                              SPECIAL TAX ELECTIONS

                  1. Stock Withholding.  Optionee is hereby granted the election
to have the Corporation withhold, at the time the option is exercised, a portion
of the purchased Option Shares with an aggregate Fair Market Value not to exceed
one hundred percent (100%) of the applicable Federal, state and local income and
employment tax withholding liability (the "Taxes") Optionee incurs in connection
with the option exercise.

                           Any such exercise of the election must be effected in
accordance with the following terms and conditions:

                           (i) The  election  must be made on or before the date
         the  liability  for the Taxes is  determined  (the  "Tax  Determination
         Date").

                           (ii) The election shall be irrevocable.

                           (iii) The  election  shall be subject to the approval
         of the Plan  Administrator,  and  none of the  Option  Shares  shall be
         withheld  in  satisfaction  of the  Taxes,  except  to the  extent  the
         election is approved by the Plan Administrator.

                           (iv)  The  Option  Shares  withheld  pursuant  to the
         election shall be valued at Fair Market Value on the Tax  Determination
         Date.

                           (v) In no event  may the  number  of shares of Common
         Stock  requested to be withheld  exceed in Fair Market Value the dollar
         amount of the Taxes.

                           If the stock withholding election is made by Optionee
at a time when Optionee is an officer or director of the Corporation  subject to
the short-swing profit




restrictions  of  Section  16(b) of the  Securities  Exchange  Act of  1934,  as
amended,  then  the  following   limitations,   in  addition  to  the  preceding
provisions, shall also be applicable:

                           (i) The  election  shall not become  effective at any
         time prior to the expiration of the six (6)-month  period measured from
         the Effective  Date of this  Addendum  indicated  below,  and no Option
         Shares shall be withheld in connection with any Tax Determination  Date
         which occurs before the expiration of such six (6)-month period.

                           (ii) The stock  withholding  election must be made in
         accordance with the following limitations:

                                  (A) Such  election  must be made at least  six
         (6) months before the Tax Determination Date, or

                                  (B) Both the exercise of such election and the
         exercise  of the option  must  occur  concurrently  within a  quarterly
         "window"  period.  Quarterly  window  periods  shall begin on the third
         (3rd)  business  day  following  the  date of  public  release  of each
         quarterly or annual statement of the  Corporation's  sales and earnings
         and end on the earlier of the twelfth  (12th)  business  day  following
         such release date or the Tax Determination Date.

                  2. Stock Delivery.  Optionee is hereby granted the election to
deliver, at the time the option is exercised, one or more shares of Common Stock
previously  acquired by Optionee  (other than in connection with the acquisition
triggering  the Taxes) with an  aggregate  Fair  Market  Value not to exceed one
hundred percent (100%) of the Taxes.

                           Any such exercise of the election must be effected in
accordance with the following terms and conditions:

                           (i) The  election  must be made on or before  the Tax
         Determination Date for the Taxes.

                           (ii) The election shall be irrevocable.

                           (iii) The  election  shall be subject to the approval
         of the Plan  Administrator,  and none of the delivered shares of Common
         Stock  shall be accepted in  satisfaction  of the Taxes,  except to the
         extent the election is approved by the Plan Administrator.

                           (iv)  The  shares  of  Common   Stock   delivered  in
         satisfaction  of the Taxes shall be valued at Fair Market  Value on the
         Tax Determination Date.

                                       2.



                           (v) In no event may the  number of  delivered  shares
         exceed in Fair Market Value the dollar amount of the Taxes.


                  IN WITNESS WHEREOF, Atlantic Pharmaceuticals,  Inc. has caused
this Addendum to be executed by its  duly-authorized  officer,  and Optionee has
executed this Addendum, all as of the Effective Date specified below.


                                       ATLANTIC PHARMACEUTICALS, INC.

                                       By:    __________________________________

                                       Title: __________________________________


                                       _________________________________________
                                       OPTIONEE



EFFECTIVE DATE:________________, 199__


                                       3.