Exhibit 4.2

     AMENDMENT TO RIGHTS  AGREEMENT  dated  September  30,  1997,  to the Rights
Agreement  dated August 6, 1991,  as amended (the  "Rights  Agreement"),  by and
between   Pharmaceutical   Resources,   Inc.,  a  New  Jersey  corporation  (the
"Company"),  and First  City  Transfer  Company  (the  "Rights  Agreement"),  as
successor to Midlantic Bank.

     WHEREAS,  the  Board of  Directors  of the  Company,  on  August  6,  1991,
authorized and adopted a share purchase  rights plan (the "Plan") to protect the
Company's  shareholders  against  unsolicited  and  hostile  attempts to acquire
control of the Company and, in connection therewith,  executed and delivered the
Rights Agreement to effectuate the terms of the Plan;

     WHEREAS,  the Plan was amended,  on March 23, 1995, in  contemplation  of a
certain negotiated transaction with Clal Pharmaceutical Industries Ltd.;

     WHEREAS,  the Board of Directors of the Company, on July 28, 1997, approved
an amendment to the Plan as described  herein in  contemplation of modifications
to such negotiated transaction;

     WHEREAS,  the Board of Directors of the Company authorized and directed the
proper  officers  of the  Company  as well as the Rights  Agent to  execute  and
deliver  this  Amendment  to the Rights  Agreement  in order to  effectuate  the
foregoing amendments to the Plan; and

     WHEREAS, all capitalized terms used herein and not otherwise defined herein
shall have the meanings set forth in the Rights Agreement.

     NOW, THEREFORE,  in consideration of the premises,  the Rights Agreement is
hereby amended as follows:

     Section (C) Certain  Definitions.  Section 1(a)(v) of the Rights  Agreement
shall be amended in its entirety as follows:

         "(v) Clal  Pharmaceutical  Industries  Ltd. and its  permitted  assigns
         under Section 16 of the Stock Purchase Agreement, dated March 25, 1995,
         between the Company and Clal Pharmaceutical Industries Ltd., as amended
         (the "Stock Purchase Agreement") (Clal  Pharmaceutical  Industries Ltd.
         and its permitted  assigns under such Section 16 shall be  collectively
         referred to herein as  "Clal"),  so long as any  acquisition  or tender
         offer by Clal is permitted under the Stock Purchase Agreement"

     (A) The  definition  of  "Permitted  Offer" in  Section  1(n) of the Rights
Agreement shall be amended in its entirety as follows:

         "(n) "Permitted Offer" shall mean the following tender
         offers made in the manner prescribed by Section 14(d) of

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         the Exchange Act and the rules and regulations  promulgated thereunder:
         (i) a  tender  offer  for  all  outstanding  Common  Shares;  provided,
         however,  that such  tender  offer  occurs  at a time  when  Continuing
         Directors are in office and a majority of the Continuing  Directors has
         determined  that  the  offer  is fair  to,  and  otherwise  in the best
         interests of, the Company and its stockholders, and (ii) a tender offer
         for Common Shares as permitted by the Stock Purchase Agreement."

     (B) The  proviso  in the  definition  of  "Section  11(a)(ii)(A)  Event" in
Section  1(v) of the  Rights  Agreement  shall be  amended  in its  entirety  as
follows:

         ";  provided,  however,  in no event shall an  acquisition of or tender
         offer for Common Shares by Clal constitute a Section 11(a)(ii)(A) Event
         until such time as any such  acquisition  or tender offer by Clal shall
         no longer be permitted under the Stock Purchase Agreement"

     (C) The proviso in the  definition of "Section 13 Event" in Section 1(w) of
the Rights Agreement shall be amended in its entirety as follows:

         ";  provided,  however,  in no event shall an  acquisition of or tender
         offer for Common  shares by Clal  constitute  a Section 13 Event  until
         such  time as any such  acquisition  or tender  offer by Clal  shall no
         longer be permitted under the Stock Purchase Agreement"

     Section (D) Authority for  Amendment.  This Amendment is being executed and
delivered as of the date hereof by the Company and the Rights Agent  pursuant to
and in accordance  with Section 27 of the Rights  Agreement.  By executing  this
Amendment,  the Company hereby certifies to the Rights Agent that this Amendment
is in compliance  with Section 27 of the Rights  Agreement.  Except as otherwise
amended hereby,  all the provisions of the Rights Agreement shall remain in full
force and effect.  This Amendment  shall be deemed to be a part of, and shall be
construed as part of, the Rights Agreement.

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     IN WITNESS  WHEREOF,  the parties  hereby have caused this  Amendment to be
duly executed as of the date first above written.


                                                 PHARMACEUTICAL RESOURCES, INC.



                                                 By: /s/ Kenneth I. Sawyer
                                                 ------------------------------
                                                 Title: President


                                                 FIRST CITY TRANSFER COMPANY



                                                 By: /s/ Kathleen M. Zaleske
                                                 ------------------------------
                                                 Title: Assistant Vice President

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