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

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                             REVOLVING TERM NOTE

                                                              December 21, 1998

$5,000,000                                                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
Five Million Dollars ($5,000,000) or such lesser amount as may be outstanding
under 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"),
an or before December 1, 2000, with interest from the date hereof on the said
principal balance from time to time outstanding. This Note and that certain
Amended and Restated Revolving Term Note from the Borrower to BBH in the face
amount of $5,000,000 dated the date hereof comprise the "Revolving 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 and interest shall be payable to the Administrative Agent
for the account of the Payee at the Administrative Agent's 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.

       This Note is a revolving note and subject to the foregoing, the
Borrower may, at its option, at any time prior to demand borrow, pay, prepay
and reborrow hereunder, all in accordance with the provisions hereof and of
any and all other agreements between the Borrower and the Lenders related
hereto; provided, however, that the principal balance outstanding shall at no
time exceed the face amount of this Note.

       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.

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       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 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 on 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

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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 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 person 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

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(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
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 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/ Barry Plost                         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.                                       December 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
                                                              ------------

                                                        [SEAL]



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