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                                                                   Exhibit 10.4


                               PROMISSORY NOTE

$150,000.00                                             Los Angeles, California
                                                              November 10, 2000

        1.  PRINCIPAL. FOR VALUE RECEIVED, the undersigned, SeraCare, Inc., a
Delaware corporation ("Maker"), hereby promises to pay to David Barrett
Inc., ("Holder"), or his/her/its order or successors or assigns, at SeraCare,
Inc., 1925 Century Park East, Suite 1970, Los Angeles, California 90067, or
at such other place as Holder may from time to time designate, in lawful
money of the United States of America, the principal sum of One Hundred Fifty
Thousand dollars ($150,000.00) (the "Principal Sum"), together with interest
on the unpaid balance accrued from the date first written above at a rate
equal to ten percent (10%) per annum, with a minimum interest charge of
$1,500.00, all in accordance with the terms of this Promissory Note (the
"Note").

        2.  In consideration for the loan the Company shall issue to the
Bridge Lender an aggregate of 37,500 warrants to purchase common stock of the
Company (the "WARRANTS"). Each Warrant shall permit the holder to purchase
shares of the Company at an initial purchase price of $3.125 per share and
shall be exercisable for five years. Such Warrants shall contain standard
cashless exercise provisions and shall be in the form attached hereto.

        3.  PAYMENT. Unless sooner accelerated pursuant to the terms of this
Note, interest accrued on the Principal Sum shall become due and payable on
December 10, 2000.

        4.  PREPAYMENT. Maker may, at any time and from time to time,
without penalty, make prepayments on the Principal Sum.

        5.  EVENT OF DEFAULT. As used herein, an "Event of Default" shall be
defined as the failure of Maker to make any payment of principal or interest
when due under the terms of this Note, such failure continuing for a period
of thirty (30) calendar days after the due date without being cured. Upon the
occurrence of an Event of Default, the unpaid principal balance of this Note
and all interest accrued thereon may, at Holder's option, at any time
thereafter be accelerated and be declared to be immediately due and payable.

        6.  INTEREST RATE LIMITATION. It is the intent of Maker and Holder
that none of the terms and provisions contained herein shall be construed to
create a contract for use, forbearance or detention of money requiring the
payment of interest at a rate in excess of the maximum interest rate
permitted by applicable law. If any Holder of this Note shall collect monies
which are deemed to constitute interest which would otherwise increase the
effective interest rate of this Note to a rate in excess of the maximum rate
permitted to be charged by

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applicable law, all such sums deemed to constitute interest in excess of such
maximum rate shall, at the option of Holder, be credited to the payment of the
sums due hereunder or returned to Maker.

        7.  SECURITY. This Note shall be secured by all of the assets,
tangible and intangible, of Maker set forth on Exhibit A hereto.

        8.  WAIVER. No delay or omission on the part of Holder hereof in
exercising any right under this Note shall operate as a waiver of such right.
Moreover, a waiver of any term or condition contained under this Note by
Holder must be in writing to be effective and shall not be construed as a
waiver of any subsequent breach or failure of the same term or condition or
of any other term or condition contained in this Note.

        9.  AMENDMENTS. Neither this Note nor any provision hereof may be
changed, waived, discharged or terminated orally, but only by an instrument
in writing signed by the party against whom enforcement of the change,
waiver, discharge or termination is sought.

       10.  SUCCESSORS. This Note shall be binding upon and inure to the
benefit of the parties hereto and their respective successors and permitted
assigns. Maker may not assign or transfer all or any part of its rights or
obligations hereunder.

       11.  COSTS OF COLLECTION. Maker promises to pay all costs and
expenses, including reasonable attorneys' fees, incurred in connection with
the collection and enforcement of this Note. Maker hereby waives diligence,
presentment, protest, demand and notice of every kind, to the fullest extent
permitted by law, and the right to plead any statute of limitations as a
defense to any demand hereunder.

       12.  GOVERNING LAW. This Note shall be governed by, and construed and
enforced in accordance with, the laws of the State of California, without
regard to conflicts of laws principles.

        13.  DRAFTING. Maker hereby waives the benefit of any statute or
rule of law or judicial decision, which would otherwise require that the
provisions of this Note be construed or interpreted most strongly against the
party responsible for the drafting thereof.

        14.  SEVERABILITY. If any provision of this Note is held to be
unenforceable for any reason, it shall be adjusted rather than voided, if
possible, to achieve the intent of the parties to the extent possible. In any
event, if any term of this Note, or the application thereof to any person,
entity or circumstance, shall, to any extent, be invalid or unenforceable,
the remainder of this Note, or the application of such term to persons,
entities or circumstances other than those as to which it is invalid or
unenforceable, shall not be affected thereby, and each term of this Note
shall be valid and enforceable to the fullest extent permitted by law.

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        15.  HEADINGS. Headings at the beginning of each numbered paragraph
of this Note are intended solely for convenience and are not to be deemed or
construed to be part of this Note.

        16.  ENTIRE AGREEMENT. This Note sets forth the entire agreement and
understanding of the parties with respect to the subject matter hereof and
supersedes all prior agreements, arrangements and understandings with respect
to the subject matter hereof. No representation, promise, oral or written
agreement, understanding, inducement or statement of intention has been made
by Maker or Holder with respect to this Note which is not embodied in this
Note. Neither Maker nor Holder shall be bound by or liable for any alleged
representation, promise, oral or written agreement, understanding, inducement
or statement of intention with respect to this Note not so set forth.

        IN WITNESS WHEREOF, the undersigned has executed this Note as of the
day and year first written above.


                                         MAKER:


                                         SERACARE, INC.,
                                         AN DELAWARE CORPORATION


                                             /S/ JERRY L. BURDICK
                                         -------------------------------------
                                         BY:     JERRY L. BURDICK
                                         TITLE:  EXECUTIVE VICE PRESIDENT


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                         LIST OF OMITTED EXHIBITS



The following Exhibit to the Secured Promissory Note between SeraCare, Inc.
("Maker") and David Barrett Inc. ("Holder") in the amount of $150,000.00,
dated November 10, 2000, has been omitted from this Exhibit and shall be
furnished supplementally to the Commission upon request:



Exhibit A      Secured Assets