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4.20  TERM PROMISSORY NOTE BETWEEN AND SERACARE, INC. AND STATE STREET BANK &
      TRUST COMPANY DATED DECEMBER 21, 1998.


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                                 TERM PROMISSORY NOTE

                                                            December 21, 1998
$3,500,000                                              Boston, Massachusetts

     For value received, the undersigned SeraCare, Inc. (the "Borrower"),
promises to pay to State Street Bank and Trust Company (hereinafter sometimes
referred to as "State Street" and "Payee"), or order, the principal amount of
Three Million Five Hundred Thousand Dollars ($3,500,000). This Note is executed
pursuant to that certain Revolving Credit, Term Loan and Security Agreement,
dated as of even date herewith (the "Loan Agreement"), among the Borrower, Avre
Incorporated, Binary Associates, Inc., SeraCare Acquisitions, Inc., BHM Labs,
Inc., SeraCare Technology, Inc., The Western States Group, Inc., American
Plasma, Inc., Brown Brothers Harriman & Co. ("BBH"), State Street and Brown
Brothers Harriman & Co. as Administrative Agent (the "Administrative Agent").
This Note and that certain Term Promissory Note from the Borrower to BBH in the
face amount of $3,500,000 dated the date hereof comprise the "Term Note" as
defined in the Loan Agreement. The aggregate principal balance outstanding under
this Note shall bear interest thereon at a per annum rate equal to the Wall
Street Journal Prime Rate (as hereinafter defined) plus three-quarters of one
percent (0.75%), payable quarterly in arrears on the first business day of each
fiscal quarter, commencing March 1, 1999. BBH and State Street are hereinafter
collectively referred to as the "Lenders." Capitalized terms used but not
defined herein are as defined in the Loan Agreement.

     "Wall Street Journal Prime Rate" means the highest rate published from time
to time by the Wall Street Journal as the Prime Rate, or, in the event the Wall
Street Journal ceases to publish the Prime Rate, the base, reference or other
rate then designated by the Payee for general commercial loan reference
purposes, it being understood that such rate is a reference rate, not
necessarily the lowest, established from time to time, which serves as the basis
upon which effective interest rates are calculated for loans making reference
thereto. The effective interest rate applicable to undersigned's loans shall
change on the date of each change in the Wall Street Journal Prime Rate.

     Principal shall be due and payable in arrears under this Note as follows:

     1.   During the first year of the term of this Note,

          (a)       $250,000 on June 1, 1999;

          (b)       $125,000 on September 1, 1999; and

          (c)       $125,000 on December 1, 1999.

     2.   During the second year of the term of this Note,

          (a)       $312,500 on March 1, 2000;

          (b)       $312,500 on June 1, 2000;

          (c)       $312,500 on September 1, 2000; and

          (d)       $312,500 on December 1, 2000.


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     3.   During the third year of the term of this Note,

          (a)       $437,500 on March 1, 2001;

          (b)       $437,500 on June 1, 2001;

          (c)       $437,500 on September 1, 2001; and

          (d)       $437,500, plus any interest then remaining
                    unpaid, due and payable, on December 1, 2001.

     In addition to all amounts due and payable in accordance with this Note,
the Borrower shall make annual prepayments of the principal balance outstanding
respecting this Note an the last day of May of each year commencing May 31, 2000
in an amount equal to the Excess Cash Flow Amount (as hereinafter defined) x
 .50. The "Excess Cash Flow Amount" shall mean a number calculated by multiplying
the Excess Cash Flow Percentage (as hereinafter defined) by the Excess Cash
Flow, "Excess Cash Flow" shall mean the Borrower's EBITDA for the Borrower's
latest fiscal year ending prior to the date any payment is due under this
paragraph (the "Applicable Period"), minus, for the Applicable Period, (i)
Borrower's capital expenditures, (ii) the Borrower's cash tax payments, (iii)
payments made by the Borrower on account of scheduled amortization and voluntary
permanent reduction of indebtedness owing to the Lenders, and (iv) cash interest
payments. "Excess Cash Flow Percentage" shall mean thirty percent (30%). All
terms used in this paragraph shall be defined in accordance with generally
accepted accounting principles consistently applied. Mandatory and voluntary
prepayments shall be applied against unpaid installments of principal of this
Note in inverse order of maturity of such installments.

     Principal and interest shall be payable to the Administrative Agent for the
account of the Payee at the Administrative Agent's main office at 40 Water
Street, Boston, Massachusetts 02109 (or at such other place as the
Administrative Agent may hereafter direct the Borrower) in lawful money of the
United States of America without set-off, deduction or counterclaim. Interest
shall be calculated on the basis of actual number of days elapsed and a 360-day
year.

     This Note is issued pursuant to, is entitled to the benefits of, and is
subject to, the provisions of the Loan Agreement, but neither this reference to
the Loan Agreement nor any provision thereof shall affect or impair the absolute
and unconditional obligation of the Borrower to pay the principal of and
interest on this Note as herein provided.

     At the option of the holder, this Note shall become immediately due and
payable without notice or demand upon the occurrence of an Event of Default
under the Loan Agreement.

     Any payments received by the Administrative Agent and Payee on account
of this Note shall be applied first, to any costs, expenses or charges then
owed to the Payee and the Administrative Agent by the Borrower; second, to
accrued and unpaid interest; and third, to the unpaid principal balance
hereof. The Borrower hereby authorizes the Payee to charge any deposit
account which the Borrower may maintain with the Payee for any payment
required hereunder.

     The Borrower represents to the Administrative Agent and the Payee that the
proceeds of this Note will not be used for personal, family or household
purposes.

     Any and all deposits or other sums at any time credited by or due to the
undersigned or any endorser or guarantor hereof from the Payee or any of its
banking or lending affiliates or any lender acting as a participant under any
loan arrangement between the Payee and the Borrower, any endorser or guarantor
hereof, and any cash, securities, instruments or other property of the
undersigned in the possession of the Payee or any of its banking or lending
affiliates or any lender acting as a participant under any loan arrangement
between the Payee and the Borrower, any endorser or guarantor hereof, whether
for safekeeping or otherwise, or in transit to or from the Payee or any of its
banking or lending affiliates or any such participant, or in the possession of
any third party acting on the Payee's behalf (regardless of the


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reason the Payee had received same or whether the Payee has conditionally
released the same) shall at all times constitute security for all of the
liabilities and obligations of the undersigned and any endorser and guarantor
hereof to the Payee and may be applied or set off against such liabilities
and obligations of the undersigned or any endorser or guarantor hereof to the
Payee at any time, whether or not such are then due, whether or not demand
has been made and whether or not other collateral is then available to the
Payee.

     No delay or omission on the part of the holder in exercising any right
hereunder shall operate as a waiver of such right or of any other right of such
holder, nor shall any delay, omission or waiver an any one occasion be deemed a
bar to or waiver of the same or any other right on any future occasion. The
Borrower and every other maker and every endorser or guarantor of this Note,
regardless of the time, order or place of signing, waives presentment, demand,
protest and notices of every kind and assents to any extension or postponement
of the time of payment or any other indulgence, to any substitution, exchange or
release of collateral, and to the addition or release of any other party or
person primarily or secondarily liable. The Borrower and each endorser and
guarantor of this Note waive any rights to any homestead exemptions on record as
of the date of this Note respecting any premises under the provisions of Chapter
188, Section 1, of the General Laws of Massachusetts.

     The Borrower and each endorser and guarantor of this Note shall indemnify,
defend and hold the Payee, the Administrative Agent and their directors,
officers, employees, agents and attorneys harmless against any claim (as well as
from attorneys' reasonable fees and expenses in connection therewith) brought or
threatened against the Administrative Agent or the Payee by the Borrower, by any
endorser or guarantor, or by any other person on account of the Administrative
Agent's or the Payee's relationship with the Borrower or any endorser or
guarantor hereof (each of which may be defended, compromised, settled or pursued
by the Administrative Agent with counsel of the Administrative Agent's
selection, but at the expense of the Borrower and any endorser and/or
guarantor), except (a) in the case of the indemnification of the Administrative
Agent against a claim brought or threatened against the Administrative Agent,
for any claim arising out of the gross negligence or willful misconduct of the
Administrative Agent, as adjudged by a court of competent jurisdiction, and (b)
in the case of the indemnification of Payee against a claim brought or
threatened against Payee, for any claim arising out of the gross negligence or
willful misconduct of Payee, as adjudged by a court of competent jurisdiction,
and (c) in the case of the indemnification of the Administrative Agent or Payee
against a claim brought against the Administrative Agent by Payee or against
Payee by the other Lender or by the Administrative Agent. The within
indemnification shall survive payment of the Obligations, and/or any
termination, release or discharge executed by the Administrative Agent or Payee
in favor of any Obligor. For purposes of clarification, no Obligor shall have
any obligation to indemnify the Administrative Agent or Payee against any claim
brought or threatened against the Administrative Agent or Payee that any Obligor
believes arises out of the gross negligence or willful misconduct of the
Administrative Agent or Payee if a court of competent jurisdiction has
determined that such claim in fact arose out of the gross negligence or willful
misconduct of the Administrative Agent or Payee, as the case may be. The Payee
shall be severally liable to refund any amounts actually and voluntarily paid by
the Obligors to the Administrative Agent with respect to any such claim,
promptly after such judicial determination. Notwithstanding any provision in
this Agreement to the contrary, the Payee and Administrative Agent agree that
neither the Payee nor the Administrative Agent shall (1) declare an Event of
Default or accelerate the Obligations or (2) set aside or reserve any Collateral
or otherwise exercise any remedies with respect to any Collateral, in each case
based solely upon an Obligor's failure to pay the amount of any indemnifiable
claim (and/or attorneys' fees and expenses in connection therewith) prior to
such judicial determination, PROVIDED, HOWEVER, that in the case of an Event of
Default (other than the failure to pay the amount of any indemnifiable claim
and/or attorneys' fees and expenses in connection therewith prior to such
judicial determination), the Payee and the Administrative Agent may accelerate
the Obligations and set aside or reserve any Collateral or otherwise exercise
any remedies with respect to any Collateral. Notwithstanding any provision in
this Agreement to the contrary, in no circumstance shall the Administrative
Agent or Payee seek consequential, punitive or any other additional damages
based upon the failure or the alleged failure of


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any Obligor to pay the amount of any indemnifiable claim and/or attorneys'
fees and expenses in connection therewith prior to such judicial
determination.

     The Borrower and each endorser and guarantor of this Note agree to pay to
the Administrative Agent and the Payee, upon demand, costs of collection of the
principal of and interest on this Note, including, without limitation,
reasonable attorneys' fees. After demand, interest shall accrue at a rate per
annum equal to the aggregate of four percent (4%) plus the rate provided for
herein. If any payment due under this Note is unpaid for ten (10) days or more,
the Borrower shall pay, in addition to any other sums due under this Note (and
without limiting the holder's other remedies on account thereof), a late charge
equal to five percent (5%) of such unpaid amount.

     This Note shall be binding upon the Borrower and each endorser and
guarantor hereof and upon their respective heirs, successors, assigns and legal
representatives, and shall inure to the benefit of the Administrative Agent and
the Payee and their successors, endorsees and assigns.

     The liabilities of the Borrower and any endorser or guarantor of this Note
are joint and several; provided, however, the release by the Payee of the
Borrower or any one or more endorser or guarantor shall not release any other
person obligated on account of this Note. Any and all present and future debts
of the Borrower to any endorser or guarantor of this Note are subordinated to
the full payment and performance of all present and future debts and obligations
of the Borrower to the Lenders. Each reference in this Note to the Borrower, any
endorser, and any guarantor, is to such person individually and also to all such
persons jointly. No person obligated on account of this Note may seek
contribution from any other person also obligated, unless and until all
liabilities, obligations and indebtedness to the Lenders of the persons from
whom contribution is sought have been satisfied in full. The release or
compromise by the Administrative Agent or the Payee of any collateral shall not
release any person obligated on account of this Note.

     A photographic or other reproduction of this Note may be made by the
Administrative Agent or the Payee if marked "copy' or "duplicate" or with any
similar designation, and any such reproduction shall be admissible in evidence
with the same effect of the original itself in any judicial or administrative
proceeding, whether or not the original is in existence.

     This Note is delivered to the Payee at one of its offices in Massachusetts,
shall be governed by the laws of the Commonwealth of Massachusetts, and shall
take effect as a sealed instrument.

     Each of the Borrower and any endorser and guarantor of this Note
irrevocably submits to the nonexclusive jurisdiction of any federal or state
court sitting in Massachusetts, over any suit, action or proceeding arising out
of or relating to this Note. Each of the Borrower and any endorser and guarantor
irrevocably waives, to the fullest extent it may effectively do so under
applicable law, any objection it may now or hereafter have to the laying of the
venue of any such suit, action or proceeding brought in any such court and any
claim that the same has been brought in an inconvenient forum. Each of the
Borrower and any endorser and guarantor irrevocably appoints the Secretary of
State of the Commonwealth of Massachusetts as its authorized agent to accept and
acknowledge on its behalf any and all process which may be served in any such
suit, action or proceeding, consents to such process being served (i) by mailing
a copy thereof by registered or certified mail, postage prepaid, return receipt
requested, to such Borrower's, endorser's or guarantor's address shown below or
as notified to the Administrative Agent and (ii) by serving the same upon such
agent, and agrees that such service shall in every respect be deemed effective
service upon such Borrower, endorser or guarantor.

     EACH OF THE BORROWER, PAYEE, ADMINISTRATIVE AGENT AND ANY ENDORSER AND
GUARANTOR HEREBY KNOWINGLY, VOLUNTARILY AND INTENTIONALLY, AND AFTER AN
OPPORTUNITY TO CONSULT WITH LEGAL COUNSEL, WAIVES ANY AND ALL RIGHTS TO A TRIAL
BY JURY IN ANY ACTION OR PROCEEDING IN CONNECTION WITH THIS NOTE, ALL OF THE
OBLIGATIONS OF THE BORROWER TO THE PAYEE, AND ALL MATTERS CONTEMPLATED HEREBY
AND DOCUMENTS EXECUTED IN CONNECTION HEREWITH. EACH OF THE BORROWER


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AND ANY ENDORSER AND GUARANTOR CERTIFIES THAT NEITHER THE ADMINISTRATIVE AGENT
NOR THE PAYEE NOR ANY OF THEIR REPRESENTATIVES, AGENTS OR COUNSEL HAS
REPRESENTED, EXPRESSLY OR OTHERWISE, THAT THE PAYEE OR THE ADMINISTRATIVE AGENT
WOULD NOT IN THE EVENT OF ANY SUCH PROCEEDING SEEK TO ENFORCE THIS WAIVER OF
RIGHT TO TRIAL BY JURY.

                              [INTENTIONALLY LEFT BLANK]


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     Executed as an instrument under seal as of December 21, 1998.

Witness                                Borrower

                                       SeraCare, Inc.

/s/ [ILLEGIBLE]                        By:  /s/ Jerry L. Burdick
----------------------                      -----------------------------------
                                            Jerry L. Burdick
                                            Executive Vice President and
                                            Chief Financial Officer

                                       1925 Century Park East, Suite 1970
                                       Los Angeles, California
                                       90067



                              STATE OF CALIFORNIA

Los Angeles, SS.                                                   Dec. 21, 1998

     Then personally appeared the above-named Jerry L. Burdick, Executive
Vice President and Chief Financial Officer of SeraCare, Inc., and
acknowledged the foregoing instrument to be the free act and deed of
SeraCare, Inc., before me,

                                                /s/ Nancy Pau, Notary Public
                                                My Commission expires: 2/19/2000


                                                             [STAMP]