EXHIBIT 99.1

[BIOSOURCE LOGO]

                                                         Chief Financial Officer
                                                   BioSource International, Inc.
                                                            chuckb@biosource.com
                                                                  (805) 383-5249




BIOSOURCE INTERNATIONAL, INC. ANNOUNCES THIRD QUARTER 2003 FINANCIAL RESULTS

CAMARILLO, CALIF.  - NOVEMBER 7, 2003

BioSource  International,  Inc.  (NASDAQ:BIOI),  announced  today its  operating
results for the third quarter and nine months ended September 30, 2003.

RESULTS FOR THE THREE MONTHS ENDED SEPTEMBER 30, 2003:

Net sales for the three months ended  September 30, 2003 were $10.7 million,  an
increase of  $600,000,  or 6%,  compared to net sales for the three months ended
September 30, 2002 and the net loss for the quarter ended September 30, 2003 was
$81,000 compared to a net income of $951,000 for the comparable  period in 2002.
Negatively  affecting  the third quarter 2003  operating  results was a $235,000
charge for costs incurred in connection with the previously announced indefinite
leave of absence and resignation of Mr. Len Hendrickson,  the Company's previous
CEO.  Affecting the net income for the three months ended September 30, 2002 was
a favorable  adjustment of $423,000 due to an arbitration  settlement  impacting
the Company's goodwill and cumulative effect of the accounting for goodwill.

"The results of the third  quarter of 2003 for  BioSource  were a reflection  of
sluggish  July  and  August  spending   patterns  from  the  major  Biotech  and
Pharmaceutical companies and from internal activities related to Mr. Hendrickson
resigning from the Company under very unfortunate  circumstances," commented Mr.
Robert J. Weltman,  a director of the Company and former  interim  President and
Chief Executive  Officer.  "I am encouraged to see that in September and October
our sales  patterns  appeared  to be getting  back on track."  Mr.  Terrance  J.
Bieker,  the Company's  newly appointed  President and Chief  Executive  Officer
replaced Mr. Weltman on November 3, 2003.

As has been  announced  during  2003,  to better  drive  growth and focus on key
market opportunities the Company has divided its business into three core areas:
The Strategic Business Units ("SBU's") of Signal Transduction Products, Cytokine
Products,  and Custom  Products.  Signal  Transduction  Products  consist of the
proteins,  antibodies, assays and other reagents used to study internal cellular
processes. Phosphospecific antibodies and phosphoELISAs(TM) are included in this
SBU.  Cytokine  Products  include  the  proteins,  antibodies,  assays and other
reagents  that are used to  study  the  processes  by which  cells  communicate.
Interleukin,  growth factor and other biological  response modifier products are
included  in  this  group.  Custom  Products  include  oligonucleotides,  custom
peptides  and  antibodies,  cell  culture  and  clinical  diagnostics  and other
reagents not specifically categorized.

For the three months ended September 30, 2003, sales of the Company's  Signaling
product  lines grew 15%  compared to the  comparable  prior year  quarter,  from
$2,013,000 to  $2,308,000,  The Company's  sales growth in its Cytokine  product
lines for the quarter ending  September 30, 2003 was 5%, growing from $4,627,000
to  $4,862,000,  compared to the three months  ended  September  30,  2002.  The
Company's  sales





in its Custom product lines  increased 3% compared to the comparable  prior year
quarter, from $3,461,000 to $3,574,000.

The  Company's  revenues  benefited  by a  $358,000  positive  impact of foreign
exchange  for the three  months ended  September  30, 2003 when  compared to the
three months ended September 30, 2002.

"I like the Company's  strategic business unit approach and believe it will help
the Company, as well as the investment community understand our business and our
objectives,"  stated Mr.  Weltman.  "Our sales  through the first nine months of
this year have grown 11%. We are growing 34% in our Signal Transduction  product
lines and 10% in our  Cytokine  product  lines.  Both are  encouraging  numbers.
BioSource  implemented  some cost cutting  measures  during the third quarter of
2003 that helped reduced its operating  expenses from $5.9 million in the second
quarter of 2003 to $5.5  million in the third  quarter  of 2003,  excluding  the
charge of $235,000 incurred in connection with Mr. Hendrickson's departure."

Gross profit  margin was 53% for the three months ended  September  30, 2003 and
57% for the three months ended  September 30, 2002.  Lower margins in our custom
product lines,  an increase in our royalty  expense and an increase in our scrap
and obsolescence accounted for a significant portion of the margin decrease.

Research and  development  expense for the three months ended September 30, 2003
and 2002 were $1.7  million  and $1.6  million  and  represented  16% and 15% of
sales,  respectively.  The  increase  of  approximately  $100,000  reflects  the
Company's incremental investment in additional personnel and materials primarily
in the Cytokine and Signal Transduction research areas. This total investment in
the Company's  research  capabilities  has resulted in the increased  release of
higher quality and novel  products,  which has produced  increased sales in both
the Cytokine and Signaling product lines. The Company expects its fourth quarter
of 2003 R & D expenditures to be lower than levels incurred in the third quarter
of 2003 due to completed and ongoing cost reduction activities.

Selling,  marketing and administrative  expenses were $3.9 million for the three
months  ended  September  30, 2003 and $3.4  million for the three  months ended
September 30, 2002 representing 36% and 33% of sales, respectively. G&A expenses
were approximately  $300,000 higher in the three months ended September 30, 2003
when compared to the three months ended September 20, 3002, due primarily to the
charge of $235,000  related to costs incurred in connection with the resignation
of  Mr.  Hendrickson.  Sales  and  marketing  expenses  increased  approximately
$200,000 in the third quarter of 2003, compared to the third quarter of 2002 due
primarily to increased  payroll  costs and  increased  marketing  programs.  The
Company  expects its fourth  quarter  2003 run rate of SG&A  expenditures  to be
lower than levels  incurred in the third  quarter of 2003 due to  completed  and
ongoing cost reduction activities.

RESULTS FOR THE NINE MONTHS ENDED SEPTEMBER 30, 2003:

Net sales for the nine  months  ended  September  30,  2003 were a record  $33.4
million, an increase of $3.2 million, or 11%, compared to net sales for the nine
months  ended  September  30,  2002 and net  income  for the nine  months  ended
September  30,  2003 was  $346,000  compared to net loss of  $1,097,000  for the
comparable period in 2002. Through the first three quarters of 2002, the Company
recognized a non-cash  charge,  net of  applicable  income  taxes of  $2,447,000
representing the cumulative effect of a change in accounting principle resulting
from the  implementation of Financial  Accounting  Standard 142,  Accounting for
Goodwill and Other Intangible Assets. Operating income for the nine months ended
September 30, 2003 was $524,000 compared to $1,659,000 for the nine months ended
September 30, 2002.  Included in the operating results for the nine months ended
September 30, 2003 is a charge of $235,000 for costs incurred in connection with
the  previously  announced  indefinite  leave of absence and  resignation of Mr.
Hendrickson, the Company's previous CEO.

The  Company's  revenues  benefited by a $1,529,000  positive  impact of foreign
exchange for the nine months ended  September 30, 2003 when compared to the nine
months ended September 30, 2002.

For the nine months ended September 30, 2003,  sales of the Company's  Signaling
product  lines,  grew 34% compared to the  comparable  prior year  period,  from
$5,273,000 to  $7,049,000,  The Company's  sales





growth in its Cytokine  product lines for the nine months  ending  September 30,
2003 was 10%, growing from $13,871000 to $15,222000.  The Company's sales in its
Custom product lines increased 1% compared to the comparable  prior year period,
from $11,030,000 to $11,107,000.

Gross profit margin was 55% for the nine months ended September 30, 2003 and 57%
for the nine months ended September 30, 2002. The Company's  margin decreased 2%
in part due to increases in its scrap and  obsolescence and lower margins in its
custom  product  lines during the first nine months of 2003.  Lower margins from
its European operations also contributed to this margin reduction.

Research and  development  expense for the nine months ended  September 30, 2003
and 2002  were  $5.5  million  and $4.4 and  represented  17% and 14% of  sales,
respectively.  The  increase in research and  development  expenses for the nine
months  ended  September  30, 2003 when  compared to the  comparable  prior year
period  reflects the Company's  increased  expenses in additional  personnel and
materials in the cytokine and signal  transduction  research areas.  The Company
has made significant  investments in its R&D capabilities since the beginning of
2002. The result of this investment has been the release of  significantly  more
and higher quality novel  products and increased  sales in both the Cytokine and
Signaling product lines.

Selling,  marketing and administrative  expenses were $11.7 million for the nine
months  ended  September  30, 2003 and $10.6  million for the nine months  ended
September 30, 2002, representing 35% of sales for each of the periods presented.
Excluding  the charge of $235,000  related to the costs  incurred in  connection
with the resignation of Mr.  Hendrickson,  SG&A as a percentage of sales for the
nine months  ended  September  30,  2003 would be 34%. In the nine months  ended
September  30,  2003,  our G&A  expenses,  excluding  the  charge  of  $235,000,
increased  approximately $100,000 compared to the first nine months of 2002. Our
sales and  marketing  expenses  for the nine  months  ended  September  30, 2003
increased  approximately  $800,000  when  compared  to  the  nine  months  ended
September  30, 2003 due  primarily to increased  personnel  costs and  marketing
programs.

The effective tax rate for the nine months ending September 30, 2003 is 23%. The
Company's  effective  tax rate can  fluctuate  depending on a number of factors,
including the use of forecasts of the Company's  financial  performance  for the
year ended December 31, 2003 and beyond. The Company continues to benefit from R
& D and other tax credits  which when  applied to income  levels for the periods
presented is resulting in effective tax rates lower than the current  applicable
federal and state statutory rates.

"The Board of  Directors  and I are excited  that Terry has joined  BioSource as
CEO, and we are confident he will be able to guide the Company effectively going
forward,"  stated  Mr.  Weltman.  "He has  exhibited  a track  record  of strong
financial control and we are confident that he will align the Company's expenses
and investments with anticipated areas of growth and return."

"I like how the Company has positioned itself for long term financial  success,"
stated Mr. Bieker.  "We are in a market that should continue to see solid levels
of spending in the years ahead. This, along with our increased focus on our core
areas of expertise in the development and  manufacturing of signal  transduction
and cytokine  research  products,  should result in increased success for us and
our shareholders."

The Company will conduct a conference  call today,  Friday,  November 7, 2003 at
10:00 A.M.  Pacific  Time.  All  interested  parties  may call  (800)  901-5213,
reservation number 31975516 to participate in the call. In addition, the Company
will be web casting the  conference  call.  You can  participate by going to our
website at www.biosource.com and entering the investor relations' portion of the
website.

                                   ##########

         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.






                 BIOSOURCE INTERNATIONAL, INC. AND SUBSIDIARIES
                 CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS
             THREE AND NINE MONTHS ENDED SEPTEMBER 30, 2003 AND 2002
                 (Amounts in thousands, except per share data)
                                   (Unaudited)



                                            THREE MONTHS ENDED      NINE MONTHS ENDED
                                              SEPTEMBER 30,            SEPTEMBER 30,
                                            2003        2002        2003        2002
                                          --------    --------    --------    --------
                                                                    
Net sales .............................   $ 10,744      10,101      33,377      30,175
Cost of sales .........................      5,079       4,365      15,160      13,109
                                          --------    --------    --------    --------
    Gross profit ......................      5,665       5,736      18,217      17,066

Operating expenses:
    Research and development ..........      1,687       1,557       5,530       4,362
    Sales and marketing ...............      2,188       1,961       7,064       6,239
    General and administrative ........      1,729       1,394       4,664       4,325
    Amortization of intangibles .......        145         160         435         481
                                          --------    --------    --------    --------
         Total operating expenses .....      5,749       5,072      17,693      15,407
                                          --------    --------    --------    --------
Operating income (loss) ...............        (84)        664         524       1,659

Interest income (expense), net ........         (2)         21          26          82
Other expense, net ....................        (19)         (8)       (101)        (10)
                                          --------    --------    --------    --------
Income (loss) before income taxes .....       (105)        677         449       1,731
Income tax expense (benefit) ..........        (24)        149         103         381
                                          --------    --------    --------    --------
        Income (loss) before cumulative
          effect of accounting change .        (81)        528         346       1,350
Cumulative effect of accounting change
     (net of applicable income taxes of
     $1,759) ..........................       --           423        --        (2,447)
                                          --------    --------    --------    --------

Net income (loss) .....................   $    (81)        951         346      (1,097)
                                          ========    ========    ========    ========

Net income (loss) per share before
accounting change:
    Basic .............................   $  (0.01)       0.05        0.04        0.14
                                          ========    ========    ========    ========
    Diluted ...........................   $  (0.01)       0.05        0.04        0.13
                                          ========    ========    ========    ========

Net income (loss) per share:
    Basic .............................   $  (0.01)       0.10        0.04       (0.11)
                                          ========    ========    ========    ========
    Diluted ...........................   $  (0.01)       0.09        0.04       (0.11)
                                          ========    ========    ========    ========

Shares used to compute per share
amounts:
    Basic .............................      9,181       9,651       9,418       9,830
                                          ========    ========    ========    ========
    Diluted ...........................      9,181      10,029       9,729      10,289
                                          ========    ========    ========    ========






                 BIOSOURCE INTERNATIONAL, INC. AND SUBSIDIARIES
                      CONDENSED CONSOLIDATED BALANCE SHEETS
                             (Amounts in thousands)

                                                     SEPTEMBER 30,  DECEMBER 31,
                                                           2003          2002
                                                         --------      --------

                   ASSETS
Current assets:
   Cash and cash equivalents .......................     $  1,544         5,941
   Accounts receivable, less allowance
     for doubtful accounts of $221 at
     September 30, 2003 and $261 at
     December 31, 2002 .............................        7,199         6,157
   Inventories, net ................................       10,485         8,880
   Prepaid expenses and other current assets .......        1,106           538
   Deferred income taxes ...........................        2,245         1,873
                                                         --------      --------
             Total current assets ..................       22,579        23,389

Property and equipment, net ........................        6,675         7,398
Intangible assets net of accumulated
  amortization of $3,090 at September
  30, 2003 and $2,655 at December 31, 2002 .........        5,641         6,076
Goodwill ...........................................          307           307
Other assets .......................................          569           526
Deferred tax assets ................................        8,810         8,810
                                                         --------      --------
                                                         $ 44,581        46,506
                                                         ========      ========
    LIABILITIES AND STOCKHOLDERS EQUITY
Current liabilities:
   Accounts payable ................................     $  2,547         3,115
   Accrued expenses ................................        3,085         2,910
   Deferred revenue ................................          291           427
   Income tax payable ..............................          403           341
                                                         --------      --------
             Total current liabilities .............        6,326         6,793
Commitments and contingencies

Stockholders' equity:
Common stock, $.001 par value. Authorized
     20,000,000 shares:  issued and
     outstanding 9,260,020 shares at
     September 30, 2003 and 9,676,931
     at December 31, 2002 ..........................            9            10
Additional paid-in capital .........................       41,975        44,500
Accumulated deficit ................................       (3,036)       (3,382)
Accumulated other comprehensive loss ...............         (693)       (1,415)
                                                         --------      --------
             Net stockholders' equity ..............       38,255        39,713
                                                         --------      --------
                                                         $ 44,581        46,506
                                                         ========      ========