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                       AMENDMENT OF EMPLOYMENT AGREEMENT
                       ---------------------------------


     THIS AMENDMENT TO EMPLOYMENT AGREEMENT is made as of the 15 day of 
November, 1996, between ZYNAXIS, INC., a Pennsylvania corporation ("Zynaxis"), 
and MARTYN D. GREENACRE, (the "Employee").

BACKGROUND
----------

         Zynaxis and the Employee are parties to an Employment Agreement dated 
May 5, 1995 (the "Employment Agreement"). CytRx Corporation, a Delaware 
corporation ("CytRx") and Zynaxis are in the process of negotiating an Agreement
and Plan of Merger and Contribution ("Merger Agreement"), pursuant to which 
CytRx will lend money to Zynaxis and Zynaxis will become a wholly-owned 
subsidiary of Vaxcel, Inc., a wholly-owned subsidiary of CytRx. In order to 
ensure that Employee remains at Zynaxis pending the closing under the Merger 
Agreement, the parties hereto desire that the Employment Agreement be amended as
provided herein. Terms are used herein as defined in the Employment Agreement 
unless otherwise defined herein.

         NOW, THEREFORE, in consideration of the mutual covenants and promises 
contained herein and in the Employment Agreement, the parties hereto, each 
intending to be legally bound hereby, agree as follows:

TERMS
-----

1.   Employee shall continue to serve as the President and Chief Executive
     Officer of Zynaxis until the first to occur of (i) the termination of this
     employment under the terms of the Employment Agreement or (ii) the date of
     final closing (the "Closing Date") under the Merger Agreement.

2.   Since October 1, 1996, Employee has deferred, and shall continue to defer
     until the Closing Date, one-third of the Base Compensation under the
     Employment Agreement. The parties hereto acknowledge that Employee has
     deferred $9,273.39 the Base Compensation through the date hereof.

3.   Zynazis agrees, in the event of a closing of the Merger Agreement, to pay
     to Employee the following amounts, so long as Employee remains in the
     employ of Zynaxis until the Closing Date:

     (i)   An amount equal to all the Base Compensation deferred by Employee
           through the Closing Date. This amount shall be paid to the Employee
           in a lump sum on the Closing Date.

     (ii)  Severance of $29,960. This amount shall be paid to Employee in a lump
           sum on the Closing Date.


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     (iii)   Performance bonuses up to an aggregate amount of $55,000 will be 
             paid to Employee on the Closing Date, payable in accordance with 
             the following;

             A.   If Zynaxis operates within the budget limits set forth in the
                  budget attached hereto, as such budget may be altered with the
                  consent of CytRx to accommodate investments in Cauldron (the
                  "Budget"), during the period from October 1996 to March 1997,
                  a bonus of $10,000 will be paid to Employee.

             B.   If $1,200,191 of accounts payable and accrued expenses are
                  satisfied at a discount of at least $114,282 by the Closing
                  Date, a bonus of $7,000 will be paid to the Employee.

             C.   If sales of assets (including, without limitation, leasehold
                  improvements, laboratory equipment and office furniture) to
                  Adolor Corporation and other purchasers, as contemplated by
                  Exhibit A to the Liquidation Agreement Schedules 1 and 2,
                  yields at least $407,000 in gross proceeds, a bonus of $15,000
                  will be paid to Employee.

             D.   If a sublease for the 7,600 square feet at the east end of
                  Zynaxis' current headquarters is executed with a rental rate
                  not less than the current rates paid by Adolor Corporation
                  under the sublease dated May 15, 1995 between Zynaxis and
                  Adolor Corporation, for an initial term not to exceed twelve
                  months, or such space is transferred to the purchaser of the
                  Cauldron business by the Closing Date, a bonus of $8,000 will
                  be paid to Employee.

             E.   If the Zyn-Linker therapeutic technology rights are sold to
                  Phanos under the terms of the Option Agreement between Zynaxis
                  and Phanos dated September 23, 1996 for at least $525,000, a
                  bonus of $15,000 will be paid to Employee.

4.   In the event the Merger Agreement is not executed on or before November 22,
     1996, or negotiations between the parties are otherwise sooner terminated,
     this Amendment shall be null and void, and of no further force and effect,
     in which event Employee shall have no further obligation to defer any
     portion of his Base Compensation and Zynaxis shall pay to Employee, as
     promptly as possible, all unpaid deferred amounts.

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5.   Except as expressly modified hereby, the Employment Agreement is hereby 
     ratified and confirmed and remains in full force and effect.

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

                                       ZYNAXIS, INC.


                                 By: /s/ Stephen K. Reidy
                                 ------------------------
                                 Chairman, Compensation Committee


                                 /s/ Martyn D. Greenacre
                                 -----------------------
                                 President & Chief Executive Officer