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 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. All capitalized terms in this Addendum, to the extent not otherwise
defined  herein,  shall  have  the  meanings  assigned  to  them  in the  Option
Agreement.

                        INVOLUNTARY TERMINATION FOLLOWING
                                CHANGE IN CONTROL

                  1. The  exercisability of the option shall not accelerate upon
the  occurrence of a Change in Control,  and the option shall,  over  Optionee's
continued  period of Service  after the Change in  Control,  continue  to become
exercisable  for the Option  Shares in  accordance  with the  provisions  of the
Option  Agreement.  However,  immediately  upon an  Involuntary  Termination  of
Optionee's  Service within eighteen (18) months following the Change in Control,
the  exercisability  of this  option,  to the  extent  the option is at the time
outstanding but not otherwise fully exercisable,  shall automatically accelerate
so that the option shall immediately become fully exercisable for all the Option
Shares at the time subject to the option and may be exercised  for any or all of
those  shares as fully  vested  shares of Common  Stock at any time prior to the
earlier of (i) the  Expiration  Date or (ii) the  expiration of the one (1)-year
period measured from the date of the Involuntary Termination.

                  2. For purposes of this Addendum, a Change in Control shall be
deemed  to  occur in the  event  of a change  in  ownership  or  control  of the
Corporation effected through either of the following transactions:

                         (i) the  acquisition,  directly or  indirectly,  by any
         person or related  group of persons  (other than the  Corporation  or a
         person that directly or indirectly  controls,  is controlled  by, or is
         under common control with,  the  Corporation)  of beneficial  ownership
         (within the  meaning of Rule 13d-3 of the  Securities  Exchange  Act of
         1934,  as amended) of  securities  possessing  more than fifty  percent
         (50%)  of  the  total  combined  voting  power  of  the   Corporation's
         outstanding  securities  pursuant  to a tender or  exchange  offer made
         directly  to the  Corporation's  stockholders  which the Board does not
         recommend such stockholders to accept, or




                        (ii) a change in the  composition  of the  Board  over a
         period  of  thirty-six  (36)  consecutive  months  or less  such that a
         majority of the Board members ceases by reason of one or more contested
         elections  for Board  membership,  to be comprised of  individuals  who
         either (A) have been Board members  continuously since the beginning of
         such period or (B) have been elected or nominated for election as Board
         members  during such period by at least a majority of the Board members
         described  in  clause  (A) who were  still in  office  at the time such
         election or nomination was approved by the Board.

                  3. The provisions of Paragraph 1 of this Addendum shall govern
the  period  for  which  the  option  is to  remain  exercisable  following  the
Involuntary  Termination of Optionee's Service within eighteen (18) months after
the Change in Control and shall  supersede any provisions to the contrary in the
Option Agreement.

                  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___

                                       2.