<PAGE>


                  AMENDMENT to DISTRIBUTORSHIP AGREEMENT


  This Amendment Agreement (this "Amendment") is made and entered into
this    day of November 1996, by and among INVITRO INTERNATIONAL, a California
corporation ("INVITRO"), and MIRAGEN INC., a California corporation
("MIRAGEN"), with reference to that certain Distributorship Agreement between
the parties dated March 11, 1996 (the "Distributorship Agreement").

A.      The parties agree that the definition of "Institutional Markets"
        contained in paragraph B of the recitals to the Distributorship
        Agreement is hereby amended as follows:

        For the purposes of this Agreement, the term "Institutional
        Markets" shall mean (i) hospitals, birthing facilities and all
        similar obstetric facilities providing for the delivery of newborn
        infants; (ii) neonatologists, gynecologists, pediatricians, child
        birth educators, lactation consultants and other health care
        professionals providing for the professional care and education of
        pregnant women, new mothers and/or newborn infants; and (iii) any
        dissemination of sales and/or advertising materials through the
        facilities or channels of distribution represented by any of the
        above-referenced institutional markets and acceptance of orders so
        solicited. 

B.      The parties agree that Section 4.1(b) of the Distributorship Agreement
        is hereby amended to extend the minimum secure storage period from 16 to
        18 years, as follows:

                    "(b)  During the term of this Agreement and after the
        expiration of this Agreement, MIRAGEN further covenants and agrees
        to maintain and preserve in its secure freezer, or similar
        designated storage facility, all samples mailed or otherwise
        delivered to MIRAGEN resulting from the sale and use of Guardian
        DNA Products sold by INVITRO for a period of at least 18 years
        from and after the date each such sample was first received by
        MIRAGEN."

C.      The parties agree that Section 8.1 of the Distributorship Agreement is
        hereby amended to provide that minimum quantities of Guardian DNA
        Products required to be purchased by INVITRO during years one through
        three of the Distributorship Agreement, in order for INVITRO to maintain
        exclusive distribution rights to the Institutional Markets, shall be as
        follows:

<TABLE>
<CAPTION>
            Period                     Number of Units
            --------------             --------------------
            <S>                        <C>
            Year 1                      >(Symbol for greater than) 20,000
            Year 2                      >(Symbol for greater than) 36,000
            Year 3                      >(Symbol for greater than) 36,000*

</TABLE>

  *Year 3 unit minimums will be negotiated between INVITRO and MIRAGEN at
  least 120 days prior to the end of Year 2 of this Agreement.  Should the
  parties fail to agree on the number of units to be purchased in order to
  maintain INVITRO's exclusive distribution rights in
<PAGE>

  Institutional Markets, and provided INVITRO has purchased at least
  36,000 units in Year 2, MIRAGEN will not grant any other third party
  marketing and distribution rights to Guardian DNA for Institutional
  Markets unless MIRAGEN has notified INVITRO and has offered INVITRO a
  right of first refusal to such rights on terms not less favorable to
  INVITRO than offered to any proposed third party distributor.  If
  MIRAGEN extends a right of first refusal to INVITRO, INVITRO is
  obligated to accept such an offer within 10 business days after receipt
  of the same, failing which INVITRO shall be deemed to have waived such
  rights.

 
D.      The address for notifications to MIRAGEN and the zip code for
        notifications to INVITRO under Section 14.7 of the Distributorship
        Agreement are amended as follows:

        To MIRAGEN: MIRAGEN INC.
                          Attention:  Chief Financial Officer
                          6 Morgan, Suite 160
                          Irvine, California  92718
                          Facsimile No. (714) 454-1557

        To INVITRO:       INVITRO INTERNATIONAL
                          Attention: President
                          16632 Millikan Avenue
                          Irvine, California 92606
                          Facsimile No. (714) 851-4985 


  Except as expressly amended above, no other amendments to the
Distributorship Agreement are contemplated by this Amendment.

                         MIRAGEN INC.

                         By:   /s/  Kevin B. Morton
                              -----------------------------
                              Kevin B. Morton, President


                         INVITRO INTERNATIONAL

                         By:  /s/  W. Richard Ulmer
                              ------------------------------
                              W. Richard Ulmer, President








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