1
 
                                                                      EXHIBIT 99
 
                        SYNERGEN DEVELOPMENT CORPORATION
                                1885 33rd Street
                          Boulder, Colorado 80301-2546
                                  303-938-6200
                                303-441-5535 FAX
 
February 1, 1995
 
Dear Partner in Synergen Clinical Partners, L.P.:
 
     We are writing you to describe how the acquisition of Synergen affects your
investment in Synergen Clinical Partners, L.P. (the "Partnership").
 
     On December 29, 1994 a subsidiary of Amgen completed the acquisition of
Synergen for $9.25 per share, in cash. As a result, Synergen became a
wholly-owned subsidiary of Amgen, and is being renamed Amgen Boulder Inc.
Synergen Development Corporation, the general partner of the Partnership, will
remain a wholly-owned subsidiary of Amgen Boulder Inc.
 
     The Synergen warrants you were issued in connection with your purchase of a
limited partnership unit now represent, upon exercise and payment of the current
per share exercise price ($15.69 per warrant share until February 29, 1996;
$17.69 thereafter), the right to receive the merger consideration of $9.25 in
cash per warrant share.
 
     The Partnership's rights to benchmark payments and royalties related to
commercial development of interleukin-1 receptor antagonist (IL-1ra) were not
changed by the acquisition. Descriptions of those payments and royalties are
included in the January 4, 1991 Agreement of Limited Partnership which you
received when you purchased your limited partnership unit.
 
     A number of partners have inquired about possible tax losses a result of
the acquisition. Because individual tax situations vary, it is not possible to
provide any guidance on this issue. You should consult with your tax advisor to
determine what options are available to you. For your convenience, a copy of the
tax opinion on the original transaction is enclosed.
 
     A number of other inquiries were also made as to whether the acquisition
resulted in changes in the development plans for IL-1ra. At this point in time
the Amgen Boulder Inc. research and clinical staffs are reviewing the plans for
all of Synergen's product candidates, including IL-1ra. The team expects to
complete the review within a few months. For now, the Il-1ra rheumatoid
arthritis trial in Europe is continuing. Any material change in that trial will
be communicated to you in the regular reports you receive from the Partnership.
 
     We appreciate your patience during this transition period. If you have any
questions regarding this letter or any other Partnership issue, please feel free
to contact Sarah Crampton, Director of Investor Relations for Amgen Boulder
Inc., at (805) 447-3352, or Robin Stanley of Paine Webber Incorporated at (800)
433-8901.
 
                                          Very Truly Yours,
 
                                          Synergen Development Corporation
                                          General Partner of Synergen Clinical
                                          Partners, L.P.