NON-ENFORCEMENT OF PATENT RIGHTS
                                              

EFFECTIVE DATE:  March 21, 1995

PARTIES:
          Cistron Biotechnology, Inc.
          Box 3004
          10 Bloomfield Avenue
          Pine Brook, NJ 07058                        ("Cistron")

          R & D Systems, Inc.
          614 McKinley Place, N.E.
          Minneapolis, MN 55413                           ("R&D")

RECITALS:

     A.   Cistron has recently made a claim against R&D that R&D's manufacture 
and sale of the mature interleukin-1 beta ("IL-1b") gene fragments, proteins 
and the supply of its IL-1b protein as a standard in its IL-1b assay kits 
(collectively, the "Products"), infringes certain patents licensed to Cistron
(the "Patents") by New England Medical Center Hospitals, Inc., Tufts 
University, Massachusetts Institute of Technology and Wellesley College (the 
"Institutions").

     B.   The parties seek to settle such claim, without any admission of 
liability, by entering into a License and Supply Agreement entered into on    
March 21, 1995 and this Non-Enforcement of Patent Rights.

AGREEMENT:

     In consideration of the rights, obligations and mutual premises set forth 
in the License and Supply Agreement Cistron, intending to be bound thereby, 
agrees as follows:  

     Upon payment in full by R&D of the license fee specified under paragraph 
2.3 of the License and Supply Agreement, Cistron, for itself and its successors
and assigns, agrees absolutely and unconditionally not to enforce any of the 
Patent rights against R&D, its parent corporation, subsidiary or affiliate 
corporations, successors and assigns relating to R&D's manufacture and sale of
the Products on or before the Effective Date of the License and Supply 
Agreement.  However, nothing contained herein shall be construed as 
(a) granting or implying any right to R&D under any existing or future letters 
patent covering the PRECURSOR KIT or IL-1b PROTEIN (as such terms are defined 
in the License and Supply Agreement) other than those rights specifically
granted in the License and Supply Agreement or (b) implying, by estoppel, any 
agreement not to enforce its rights under the Patents for any potential future 
infringement of the Patents by R&D. Cistron represents and warrants to R&D that
it has the full, exclusive right to bring any infringement action to enforce 
the Patents.

     Cistron has caused this Release to be executed in the manner appropriate 
to it to be effective as of the date set forth above.


                                   CISTRON BIOTECHNOLOGY, INC.

                                   By /s/Bruce C. Galton  
                                     -------------------
                                     Its President & CEO