WAIVER, RELEASE AND TERMINATION AGREEMENT
        -----------------------------------------

        This Waiver, Release and Termination Agreement (the
"Agreement"), dated as of August 24, 2000, is entered into by
and between Cistron Biotechnology, Inc., a Delaware
corporation ("Cistron") and Aventis Pasteur S.A., a societe
anonyme organized under the laws of France, (formerly known as
Pasteur Merieux Serums & Vaccins, S.A.) ("AvP").
WHEREAS, Cistron and AvP have entered into that certain
Collaboration and Option Agreement, dated as of October 30,
1998 (the "COA"); and

        WHEREAS, Cistron and AvP desire to terminate the COA; and

        WHEREAS, pursuant to the terms and subject to the
conditions of that certain Common Stock and Warrant Purchase
Agreement dated October 30, 1998, by and between Cistron and
AvP (the "Purchase Agreement"), AvP acquired from Cistron a
Common Stock Purchase Warrant to purchase 666,667 shares of
Common Stock of Cistron at $0.25 per share (the "Warrant"); and

        WHEREAS, subject to the provisions of the COA, Cistron
granted to AvP an option to obtain from Cistron a license to
use Cistron inventions relating to a cytokine called
Interleukin 1 beta as an adjuvant with human vaccines (the
"Factor"), under the terms and conditions set forth in that
certain License Agreement dated October 30, 1998 (the "License
Agreement"); and

        WHEREAS, in consideration of the surrender to Cistron of
the unexercised Warrant acquired by AvP pursuant to the
Purchase Agreement and of the forgiveness by Cistron of
certain payments payable by AvP pursuant to the COA, Cistron
and AvP have agreed to execute this Agreement; and

        NOW, THEREFORE, in consideration of the foregoing and the
mutual covenants and agreements contained herein and other
good and valuable consideration, the receipt and sufficiency
of which is hereby acknowledged, the parties hereto agree as
follows:

                1. Waiver and Release by the Parties.
                   ---------------------------------
        Subject to the provisions of Sections 3, 5, 6 and 7 below,
Cistron and AvP, in consideration of the surrender by AvP of the
Warrant to Cistron without having exercised any portion thereof
and the release of AvP from further obligation under the COA,
hereby irrevocably waive any and all claims against, and
irrevocably discharge and fully release each other party to
this Agreement and all of their respective successors,
assigns, directors, officers, employees, representatives,
agents, attorneys and advisors, from any and all obligations,
liabilities, payments, claims or demands whatsoever
(collectively, "Liabilities"), to which either of them is
entitled under the COA and the Warrant, including, without
limitation, support commitment payments payable to Cistron by
AvP pursuant to the provisions of Sections 3.4.1 and 3.4.2 of
the COA and the conduct of research work by Cistron pursuant
to the provisions of Section 3.2 of the COA or the expenditure
of any funds by Cistron in connection with such research work,
this Agreement being hereby intended to settle and forever
determine any and all disputes and differences between the
parties of every nature whatsoever under the COA and the
Warrant arising prior to or after the date of this Agreement;
provided, however, the parties hereby acknowledge that nothing
set forth in this Agreement shall be, or be deemed to
constitute, a waiver, release, termination, amendment or
modification of, or otherwise affect, any other Liabilities of
the parties under any agreement or instrument other than the
COA and the Warrant.

                2. Termination.
                   -----------
        Each of Cistron and AvP hereby agree that, in consideration
of the surrender of the Warrant by AvP to Cistron without having
exercised any portion thereof and the release of AvP from further
obligation under the COA, the COA is terminated and the Warrant is
cancelled and, as of the date hereof, shall each be of no further
force and effect.

<PAGE> 2
                3. Rights to Joint Inventions.
                   --------------------------
         Each of Cistron and AvP hereby agree that to the knowledge of
each of Cistron and AvP, on and as of the date hereof, there are no
Joint Inventions (as defined in the COA).  Each of Cistron and AvP
hereby further agree however, that to the extent Joint
Inventions do exist on and as of the date hereof; (i) any
rights to such Joint Inventions shall be owned by Cistron and
AvP shall have no right to use any of such Joint Inventions,
and (ii) upon the request by Cistron, AvP shall provide such
assistance and shall execute or cause the execution of such
documentation as is reasonably necessary to effect the
transfer of any and all rights to Joint Inventions to Cistron
such that Cistron is the sole owner of such rights, and shall
provide reasonable assistance to Cistron, at Cistron's
expense, in connection with Cistron asserting or defending any
proceeding relating to the Joint Inventions.

                4. Surrender of Warrant.
                   --------------------
             Simultaneously with the execution of this Agreement,
AvP shall surrender the Warrant to a duly authorized representative
of Cistron, and Cistron shall take all action to cancel the Warrant.

                5. Support Payment for October 1, 2000 Calendar Quarter.
                   ----------------------------------------------------
            Notwithstanding any other provision of this Agreement
to the contrary, each of Cistron and AvP hereby agree that AvP
shall pay to Cistron the sum of $75,000 (the "October Support
Payment") which shall be due and payable by AvP on or about
October 1, 2000, but in no event is payable by AvP later than
October 4, 2000 (the "October Support Payment Date"),
representing the support commitment payment payable to Cistron
for the calendar quarter commencing October 1, 2000, by wire
transfer in immediately available funds to a bank account
designated in writing by Cistron at least three (3) business
days prior to the October Support Payment Date, provided,
however, that no such October Support Payment shall be payable
by AvP in the event that Cistron executes with a third party
an option, license or other agreement providing rights to the
Factor at any time prior to the October Support Payment Date
(it being acknowledged that the Agreement and Plan of Merger
dated as of March 21, 2000, as amended (the "Merger
Agreement"), by and among Cistron, Celltech Group plc and CGP
Acquisition Corp. does not constitute such an agreement).

                6. Final Support Payment.
                   ---------------------
        Notwithstanding any other provision of this Agreement
to the contrary, each of Cistron and AvP hereby agree that AvP
shall pay to Cistron the sum of $125,000 (the "Final Support Payment")
which shall be due and payable by AvP on January 2, 2001 (the "Final
Support Payment Date"), by wire transfer in immediately available
funds to a bank account designated in writing by Cistron at
least three (3) business days prior to the Final Support
Payment Date, provided, however, that no such Final Support
Payment shall be payable by AvP in the event that Cistron
executes with a third party an option, license or other
agreement providing rights to the Factor at any time prior to
the Final Support Payment Date (it being acknowledged that the
Merger Agreement does not constitute such an agreement).

                7. Survival of Confidentiality Obligations.
                   ---------------------------------------
        Notwithstanding any other provision of this Agreement to the
contrary, each of Cistron and AvP hereby agree that the obligations set
forth in the provisions of Sections 4.1(a), 4.1(b), 4.1(c) and 4.1(e) of
the COA shall survive the termination of the COA, as contemplated by
Section 4.1(d) thereof, provided, however, that neither Cistron nor AvP
shall, without the prior written consent of the other, which
shall not be unreasonably withheld, issue any press release or
make any other public announcement concerning (i) this
Agreement and the transactions contemplated hereby, or (ii)
AvP, in the case of any press release or other public
announcement made by Cistron, or Cistron, in the case of any
press release or other public announcement made by AvP.

                8. Successors and Assigns.
                   ----------------------
           This Agreement is for the benefit of the parties hereto and
their respective successors and assigns.

<PAGE> 3

                9. Entire Agreement.
                   ----------------
         This Agreement contains the entire understandings of Cistron
and AvP and supersedes all prior express or implied agreements or
understandings, either oral or written, with respect to the subject
matter hereof among such parties.  This Agreement may be amended and
the observance of any term of this Agreement may be waived with
(and only with) the written consent of Cistron and AvP.

               10. Counterparts.
                   ------------
          This Agreement may be executed in any number counterparts, each
of which shall be deemed an original and all of which together constitute
one and the same instrument.

               11. Governing Law.
                   -------------
             This Agreement shall be governed by and construed in accordance
with the laws of the State of New York without regard to principles of
conflicts of law.

<PAGE> 4

        IN WITNESS WHEREOF, the undersigned have executed this
Agreement as of the date first above written.

                                AVENTIS PASTEUR S.A.

                                By:/s/DAVID J. WILLIAMS
                                   --------------------
                                Name: DAVID J. WILLIAMS
                                Title:PRESIDENT AND COO

                                CISTRON BIOTECHNOLOGY, INC.

                                By:/s/ISIDORE S. EDELMAN,M.D.
                                   --------------------------
                                Name: ISIDORE S. EDELMAN
                                Title: CHAIRMAN AND CEO