<PAGE>

                          ASSIGNMENT OF LESSOR CLAIMS


          THIS ASSIGNMENT OF LESSOR CLAIMS ("Assignment") is entered as of the
31st day of January, 1997, by and between CHIRON CORPORATION, a Delaware
corporation ("Assignee") and BGR III ASSOCIATES, A CALIFORNIA LIMITED
PARTNERSHIP ("Assignor").

          THIS ASSIGNMENT IS ENTERED on the basis of the following facts,
intentions and understandings of the parties:

          A.   Contemporaneously with execution and delivery of this Assignment,
Assignee is acquiring certain improved real property ("Real Property"), commonly
known as the "Big O Property," in Emeryville, California pursuant to the Second
Amendment to Triple Net Lease ("Agreement") dated as of January 31, 1997,
between Assignor and Assignee.  The Real Property is more particularly described
in the Agreement.

          B.   In connection with the conveyance of the Real Property to
Assignee, Assignor and Assignee have agreed that Assignor will transfer and
assign to Assignee all of Assignor's right, title and interest in and to the
Lessor Claims (as defined in the Agreement).

          NOW, THEREFORE, in consideration of the mutual covenants, premises and
conditions herein set forth, Ten and 00/100 Dollars ($10.00) and other good and
valuable consideration, the receipt and legal sufficiency of which are hereby
acknowledged, the parties hereto, intending to be legally bound hereby, agree as
follows:

          1.   RECITALS.  The Recitals stated above are hereby incorporated
herein by reference as if fully set forth at this point in the text of this
Assignment.

          2.   TRANSFER AND ASSIGNMENT.  Assignor hereby sells, transfers,
assigns, delivers, grants and conveys to Assignee and its successors and
assigns, all right, title and interest of Assignor in and to the Lessor Claims.

          3.   CONDITIONS OF ASSIGNMENT.  Assignor's sale, transfer, assignment,
delivery, grant and conveyance of the Lessor's Claims shall be subject to the
terms of Section 12.b and 12.c. of the Agreement.

          4.   REPRESENTATION AND WARRANTY.  Assignor represents and warrants
that the Lessor Claims are free of all liens, encumbrances and claims of others,
financing agreements and/or encumbrances.


<PAGE>

          5.   HEADINGS.  The headings used in this Assignment are for purposes
of convenience only and shall not be used in construing the provisions hereof.

          6.   COVENANT OF FURTHER ASSURANCES.  The parties hereto agree to
execute such other documents and perform such other acts as may be necessary or
desirable to carry out the purposes of this Assignment.

          7.   SUCCESSORS AND ASSIGNS.  This Assignment shall bind and benefit
the personal representatives, successors and assigns of the parties hereto.

          8.   GOVERNING LAW.  This Assignment shall be governed by and
construed in accordance with the laws of the State of California.

          9.   SEVERABILITY.  The provisions of this Assignment shall be deemed
severable, and the invalidity or unenforceability of any one or more of the
provisions hereof shall not affect the validity or enforceability of the other
provisions hereof.

          10.  MODIFICATION.  This Assignment may not be modified except by the
written agreement of the parties hereto.

          11.  COUNTERPARTS.  This Assignment may be executed simultaneously in
two or more counterparts, each of which shall be deemed an original, but all of
which taken together shall constitute one and the same instrument.


                                       2.

<PAGE>


          IN WITNESS WHEREOF, the parties hereto have caused this Assignment to
be executed, on the date(s) set forth below, as of the day and year first above
written.


                                   "ASSIGNEE"

                                   Chiron Corporation, a Delaware
                                   corporation


                                   By:   /s/ Dennis L. Winger
                                        -----------------------------------

                                        Name: Dennis L. Winger
                                             ------------------------------

                                        Its:  Senior VP, Finance & Admin.
                                             ------------------------------

                                        Date: 1/30/97
                                             ------------------------------



                                   "ASSIGNOR"

                                   BGR III Associates, A California
                                   Limited Partnership


                                   By:  /s/ Richard K. Robbins
                                        -----------------------------------

                                        Name: Richard K. Robbins
                                             ------------------------------

                                        Its:  Managing General Partner
                                             ------------------------------

                                        Date: 1/28/97
                                             ------------------------------


                                       3.