BIOTIME, INC.
                                935 Pardee Street
                               Berkeley, CA 94710
                      Tel: 510-845-9535 o Fax: 510-845-7914


                                               July 29, 1999

Sheldon M. Wecker, Ph.D., Director
Hospital Products Division
Abbott Laboratories, D-977, AP30
200 Abbott Park Road
Abbott Park, IL  60064-3537

Dear Mr. Wecker:

         This is to  confirm  in  writing  a  modification  of  Article 8 of our
Exclusive License Agreement, dated April 23, 1997 (the "Agreement"), as follows.

The caption,  first  sentence and table portion of Article 8(a) of the agreement
is hereby deleted and replaced with the following:

         (a)  Minimum  Amounts.  Abbott  agrees  to  the  establishment  of  the
following  minimum  Product sales targets in the Territory for each twelve month
period,  commencing on and after October 1, 2000, subject to Abbott's option not
to market the Product as provided in 8(b) below.


[Confidential Information has been omitted and filed separately with the
  Securities and Exchange Commission]


         All other terms and  conditions of the  Agreement  remain in full force
and effect. If this  modification is acceptable,  each party shall so signify by
having an  authorized  officer  counter  sign this letter in the place  provided
below. Thank you.


                                               Very truly yours,


                                               /s/Ronald S. Barkin
                                               --------------------
                                               President and COO






ABBOTT LABORATORIES
July 29, 1999
Page 2



ACCEPTED AND AGREED:

Abbott Laboratories                                           BioTime, Inc.


By:    /s/Richard A. Gonzalez                  By:    /s/Ronald S. Barkin
       -----------------------------                  -------------------------
Title: President HPD                        Title:    President
       ---------------------------                    -------------------------
D
ate:  August 3, 1999                         Date:    July 29, 1999