<PAGE>
                                                           Exhibit 10.2

                       SECURED PROMISSORY NOTE

$150,000.00                                           Los Angeles, California
                                                             October 15, 1997


          1.   PRINCIPAL. FOR VALUE RECEIVED, the undersigned, SeraCare,
Inc., a Delaware corporation ("Maker"), hereby promises to pay to Barry D.
Plost, ("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 and 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, all in
accordance with the terms of this Promissory Note (the "Note").

          2.   PAYMENT. Unless sooner accelerated pursuant to the terms of
this Note, interest accrued on the Principal Sum shall become due and payable
on a monthly basis, with the first interest payment becoming due and payable
one month after the date first written above, and the Principal Sum, together
with any accrued and unpaid interest, shall become due and payable upon
demand by the Holder.

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

          4.   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.

          5.   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 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.

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


<PAGE>


          7.   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.

          8.   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.

          9.   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.

          10.  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.

          11.  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.

          12.  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.

          13.  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 terms 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.

          14.  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.

          15.  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

                                       2

<PAGE>


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: CHIEF FINANCIAL OFFICER

                                       3

<PAGE>


                             LIST OF OMITTED EXHIBITS


The following Exhibit to the Secured Promissory Note between SeraCare, Inc.
("Maker") and Barry D. Plost ("Holder") in the amount of $150,000.00, dated
October 15, 1997 has been omitted from this Exhibit and shall be furnished
supplementally to the Commission upon request:

Exhibit A       Secured Assets