EXHIBIT 99.1

[BIOSOURCE INTERNATIONAL LOGO]                                      Charles Best
                                                         Chief Financial Officer
                                                   BioSource International, Inc.
                                                            chuckb@biosource.com
                                                                  (805) 383-5249




BIOSOURCE INTERNATIONAL, INC.  NAMES PRESIDENT AND CHIEF EXECUTIVE OFFICER

CAMARILLO, CALIF.  - OCTOBER 20, 2003

BioSource  International,  Inc.  (Nasdaq:  BIOI -  News)  announced  today  that
Terrance J. Bieker has been elected by the Board of Directors to the position of
President and Chief Executive Officer,  commencing  November 3, 2003. Mr. Bieker
will also be appointed to fill the vacancy  created on the board of directors of
the Company by the  resignation  of Len  Hendrickson.  Mr.  Bieker  succeeds Len
Hendrickson  who,  the Company  sadly  announced on  September  11, 2003,  would
commence an indefinite medical disability leave of absence.  Mr. Robert Weltman,
a Director of BioSource, has acted as interim CEO in Mr. Hendrickson's absence.

Jean-Pierre  Conte,  the  Company's  Chairman  of the  Board,  commented  on the
announcement:  "Terry is just what BioSource needs to take us to the next level.
He has a record of  leadership  in  growing  mid-stage  reagent  and  instrument
technology  companies  and a first-hand  understanding  of providing  integrated
solutions  to meet the  needs of life  science  customers.  We  believe  Terry's
multi-faceted  successful  operating  experience  will provide us with a focused
effort  aimed  at  translating  our  well-recognized,  innovative  technological
accomplishments into successful commercial opportunities."

Terry Bieker formerly served as CEO of Axya Medical,  Inc. and President and CEO
of Transfusion Technologies  Corporation.  Also within the life sciences sector,
Mr. Bieker served as Executive  Vice  President and Chief  Operating  Officer of
Safeskin  Corporation  and  Chairman,  CEO and  President of Sanofi  Diagnostics
Pasteur.  Prior to these  appointments,  Mr. Bieker served as General Manager of
Genetic  Systems  Corporation.  His early career was with  various  divisions of
American  Hospital  Supply  Corporation.  Mr.  Bieker  holds  a B.S.  degree  in
Economics from the University of Minnesota.

"I am excited about the  opportunity to work with this energized  company," said
Mr.  Bieker.  "There is a  tremendous  opportunity  for  BioSource to become the
leader in the supply of unique and critical research biologicals to life science
researchers.  Matching our innovative reagents to customer needs and growing our
customer  base  are  keys to our  success.  We all  benefit  substantially  when
assisting the scientific community in furthering its research efforts."

                                   ##########

         BioSource  International,  Inc. is a broad based life sciences  company
focused on providing  integrated  solutions in the areas of functional genomics,
proteomics, and drug discovery through the development, manufacturing, marketing
and distribution of unique biologically active reagent systems which facilitate,
enable and accelerate pharmaceutical development and biomedical research.

This press release  contains  statements  about expected  future events that are
forward-looking and subject to risks and uncertainties. For these statements, we
claim the safe harbor for "forward-looking statements"





within the  meaning of the  Private  Securities  Litigation  Reform Act of 1995.
Factors  that could  cause  actual  results to differ and vary  materially  from
expectations  include, but are not limited to, our ability to expand our product
offerings and any transition to new products,  product quality and availability,
any change in business  conditions,  changes in our sales  strategy  and product
development plans, competitive pricing pressures, continued market acceptance of
our products, name recognition of our products, delays in the development of new
technology,  intellectual  property and  proprietary  rights may not be valid or
infringe  the  rights of others,  changes in  customer  buying  pattern  issues,
one-time events and other important factors  disclosed  previously and from time
to time in our  filings  with the  Securities  and  Exchange  Commission.  These
cautionary  statements  by us should not be  construed as  exhaustive  or as any
admission  regarding  the adequacy of  disclosures  made by us. We cannot always
predict or determine  after the fact what factors would cause actual  results to
differ  materially  from those  indicated by the  forward-looking  statements or
other  statements.  In addition,  readers are urged to consider  statements that
include  the  terms  "believes,"  "belief,"  "expects,"  "plans,"  "objectives,"
"anticipates," "intends," "targets," "projections",  or the like to be uncertain
and  forward-looking.   All  cautionary  statements  should  be  read  as  being
applicable to all  forward-looking  statements  wherever they appear.  We do not
undertake  any  obligation  to  publicly  update or revise  any  forward-looking
statements, whether as a result of new information, future events or otherwise.