THERMOGENESIS CORP.
                              3146 Gold Camp Drive
                           Rancho Cordova, California
                                 (916) 858-5100



                                                          November 15, 1999


To the Shareholders of THERMOGENESIS CORP:

        On November 8, 1999,  the Company  sent you a Notice of Annual  Meeting,
Proxy Statement, and form of proxy related to the Company's annual meeting to be
held at 10:00 a.m.,  local time, on Friday  December 10, 1999 at The Lake Natoma
Inn, located at 702 Gold Lake Drive, Folsom, California, 95630.

        The  Proxy  Statement  contains  important  information  concerning  the
election  of the Board of  Directors  and an  amendment  to the  Company's  1998
Employee Equity Incentive Plan to increase the number of shares  underlying that
Plan.  Unfortunately,  some of the information  contained in the Proxy Statement
inadvertently referred to inconsistent dates for the meeting. We wish to clarify
that the  Annual  Meeting  will be held at 10:00  a.m.,  local  time,  on Friday
December  10,  1999 at The Lake  Natoma  Inn,  located  at 702 Gold Lake  Drive,
Folsom, California, 95630.

        We urge you to give the proposals to be voted upon at the annual meeting
your close attention,  as they are of great  significance to the Company and its
shareholders,  and you should read the Proxy Statement  carefully.  The Board of
Directors strongly recommends your approval on each of these proposals.

        We hope you will be able to  attend  the  annual  meeting,  but,  if you
cannot do so, it is important that your shares be represented.  Accordingly,  we
urge you to mark,  sign,  date, and return the proxy that accompanied the Notice
of Annual Meeting and Proxy  Statement.  If you need additional Proxy Statements
or form of proxies, please contact investor relations at 916-858-5100.

                                   Sincerely,


                                   David C. Adams
                                   Secretary