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4.22  AMENDED AND RESTATED SUBORDINATION AGREEMENT BETWEEN HOLDERS OF THE 12%
      SENIOR SUBORDINATED DEBENTURES DUE 2005 OF SERACARE, INC. AND BROWN
      BROTHERS HARRIMAN & CO. AND STATE STREET BANK & TRUST COMPANY ("LENDERS")
      DATED DECEMBER 21, 1998.


<PAGE>

                    AMENDED AND RESTATED SUBORDINATION AGREEMENT

           This AGREEMENT entered into at Boston, Massachusetts, as of December
21, 1998, between the undersigned holders of the 12% Senior Subordinated
Debentures due 2005 of SeraCare, Inc. (each a "Creditor," and collectively, the
"Creditors"), Brown Brothers Harriman & Co., with an address of 40 Water Street,
Boston, Massachusetts 02109 ("BBH"), State Street Bank and Trust Company, with
an address of 225 Franklin Street, Boston, Massachusetts 02110 ("State Street")
(BBH and State Street are hereinafter collectively referred to as the "Lenders"
and sometimes individually as a "Lender"), and Brown Brothers Harriman & Co. as
Administrative Agent for the Lenders (the "Administrative Agent").

           For valuable consideration, receipt whereof is hereby acknowledged,
and in consideration of the loans, advances, discounts, renewals or extensions
now or hereafter made each by Lenders to or for the account of SeraCare, Inc.
(hereinafter called the "Borrower"), Creditors hereby agree with the Lenders and
the Administrative Agent as follows:

      1.   Creditors represent to the Lenders and the Administrative Agent that
the Borrower now owes Creditors the aggregate principal amount of $16,000,000,
together with accrued and unpaid interest, fees and expenses (the "Debenture
Indebtedness") and that the Debenture Indebtedness has not been assigned to or
subordinated in favor of any other person or entity and that Creditors hold no
security therefor. Creditors further represent that the Debenture Indebtedness
is not represented by any notes or other negotiable instruments, except that
certain 12% Senior Subordinated Debenture, dated February 13, 1998 (the
"Debenture") by the Borrower in favor of the Creditors which contains a legend
indicating that the Debenture is subordinate to the obligations owing by
Borrower to the Lenders under the Revolving Credit, Term Loan and Security
Agreement dated as of December 21, 1998, among the Borrower, the Lenders, the
Administrative Agent and various subsidiaries of the Borrower, as the same may
be amended from time to time (the "Loan Agreement"). Creditors and, by its
acknowledgment and agreement below, Borrower, agree that if at any time the
Debenture Indebtedness is evidenced by any notes, debentures, or instruments
other than the Debenture, Creditors and Borrower shall cause such notes,
debentures, or instruments to contain a legend substantially similar to the
legend contained on the Debenture.

      2.   Creditors hereby subordinate all present and future indebtedness of
the Borrower to Creditors (collectively, the "Pecks Indebtedness") to any and
all indebtedness now or hereafter owing by the Borrower to the Lenders,
including, but not limited to, any and all indebtedness in connection with the
Loan Agreement, except for any SUBORDINATED indebtedness that may hereafter be
incurred and owing by Borrower to Lenders, (collectively, the "Lender
Indebtedness") and agree not to demand, accept or receive any payment of
principal or interest upon account of the Pecks Indebtedness or any collateral
therefor, until all Lender Indebtedness has been paid in full, except for
regularly scheduled payments of principal and interest respecting the Pecks
Indebtedness, provided there is no existing event of default continuing under
the Lender Indebtedness before or as a consequence of such payment. Creditors
will not commence or join with any other creditor or creditors of Borrower in
commencing any bankruptcy, reorganization or insolvency proceedings against
Borrower. Creditors also subordinate any claims that Creditors might assert
against any guarantor of the Pecks Indebtedness to any and all claims assertable
by the Lenders (whether through the Administrative Agent or otherwise) against
guarantors of the Lender Indebtedness.

<PAGE>

      3.   Subject to the Lenders' priority of liens in the Lenders' collateral
securing the Lender Indebtedness, nothing in this Agreement shall prohibit
Creditors from taking action (except to commence or join with any other creditor
or creditors of Borrower in commencing any bankruptcy, reorganization or
insolvency proceedings against Borrower) to enforce their rights under the Pecks
Indebtedness after expiration of the Standstill Period (as hereinafter defined)
so long as there continues to be an existing uncured event of default involving
the payment of money under the Pecks Indebtedness. Standstill Period" shall
mean the period of time commencing with the date on which Administrative Agent
notifies Creditors that an event of default has occurred under the Lender
Indebtedness, provided that such event of default has not been cured or waived,
and expiring one hundred and eighty (180) days after such date. If, during the
Standstill Period, the default under the Lender Indebtedness is cured or waived,
the Standstill Period shall cease running, and a new Standstill Period shall
commence running when the Administrative Agent gives notice that an additional
event of default has occurred under the Lender Indebtedness. The Standstill
Period shall be tolled during any period of time that there is in effect an
automatic stay under the Bankruptcy Code or an injunction or restraining order
issued by a court prohibiting Lenders or the Administrative Agent from
exercising their remedies, until a court of competent jurisdiction has lifted
such stay, injunction, or restraint.

      4.   Should any payment be received by Creditors for or on account of any
of the Pecks Indebtedness in contravention of this Agreement, prior to the
satisfaction of all Lender Indebtedness, Creditors will forthwith deliver the
same to the Administrative Agent, in precisely the form received (except for
Creditors' endorsement where necessary) for application on account of the
Borrower's obligations to the Lenders and, until so delivered, the same shall be
held in trust by Creditors as the property of the Lenders.

      5.   In order to carry out the terms and the intent of this Agreement more
effectively, Creditors will do all acts and execute all further instruments
reasonably requested by the Lenders and the Administrative Agent as necessary or
convenient to preserve for the Lenders and the Administrative Agent the benefit
of this Agreement.

      6.   Creditors further waive presentment, notice and protest in connection
with all negotiable instruments evidencing the indebtedness subordinated hereby
or Borrower's indebtedness to Lenders, notice of the acceptance of this
Agreement by Lenders and the Administrative Agent, notice of any loan made,
extension granted or other action taken in reliance hereon and all demands and
notices of every kind in connection with this Agreement, or the indebtedness of
Borrower to Lenders or to Creditors; assent to any renewal, extension or
postponement of the time of payment of the Lender Indebtedness or any other
indulgence with respect thereto, to any substitution, exchange or release of
collateral therefor and to the addition or release of any person primarily or
secondarily liable thereon; and agree to the provisions of any instrument,
security or other writing evidencing the Lender Indebtedness. No action which
the Lenders or the Administrative Agent, or the Borrower with the consent of the
Lenders, may take or refrain from taking with respect to any Lender
Indebtedness, or any note or notes representing the same, or any collateral
therefor, including a waiver or release thereof or any agreement or agreements
(including guaranties) in connection therewith, shall affect this Agreement or
the obligations of Creditors hereunder. If all Lender Indebtedness is at any
time hereafter paid in full and thereafter Borrower again becomes indebted to
the Lenders, the provisions of this Agreement shall apply to said new
indebtedness unless, before the same is incurred, Creditors notify the
Administrative Agent in writing of the cancellation of this Agreement.

      7.   No waiver shall be deemed to be made any Lender or the Administrative
Agent of any of its rights hereunder unless the same shall be in writing and
shall be a waiver only with respect to the specific instance involved unless
otherwise provided for in such waiver; and it shall in no way impair any
Lender's or the Administrative Agent's rights or Creditors' obligations to it in
any other respect or any other time.

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<PAGE>

This Agreement incorporates all discussions and negotiations between Creditors
and Lenders and the Administrative Agent concerning the subordination provided
by Creditors hereby, and no such discussions or negotiations shall limit, modify
or otherwise affect the provisions hereof, and no provision hereof may be
altered, amended, waived, canceled or modified, except by a written instrument
executed and delivered by a duly authorized officer of each Lender.

      8.   The rights granted to the Lenders and the Administrative Agent
hereunder are solely for their protection and nothing herein contained shall
impose on any Lender or the Administrative Agent any duties with respect to any
property of the Borrower or Creditors received hereunder, beyond reasonable care
in its custody and preservation while in the Lenders' or the Administrative
Agent's possession. The Lenders and the Administrative Agent shall have no duty
to preserve rights against prior parties in any instrument or chattel paper
received hereunder or pursuant to this Agreement.

      9.   In the event of a conflict between the terms of this Agreement and
the terms of Section 8 of that certain Securities Purchase Agreement, dated
as of February 13, 1998, among Borrower, Avre, Incorporated, Binary
Associates, Inc., BHM Labs, Inc., SeraCare Acquisitions, Inc., SeraCare
Technology, Inc., and the Creditors, the terms of this Agreement shall
govern. This Agreement shall bind Creditors and Creditors' heirs, successors,
assigns and legal representatives and shall inure to the benefit of the
Lenders and the Administrative Agent and their successors and assigns, and
shall be governed by and construed in conformity with the laws of the
Commonwealth of Massachusetts.

                             [INTENTIONALLY LEFT BLANK]



                                          3
<PAGE>

      EXECUTED under seal as of the date first above written.

      Witness:                           Creditors:

                                         DECLARATION OF TRUST
                                         FOR DEFINED BENEFIT PLANS
                                         OF ZENECA HOLDINGS INC.

                                         DECLARATION OF TRUST
                                         FOR DEFINED BENEFIT PLANS
                                         OF ICI AMERICAN HOLDINGS INC.

                                         DELAWARE STATE EMPLOYEES'
                                         RETIREMENT FUND

                                         THE J. W. MCCONNELL FAMILY
                                         FOUNDATION

                                         By: Pecks Management Partners Ltd.,
                                         Its Investment Advisor

                                         By:       /s/ Robert J. Cresci
------------------------------           ---------------------------------
                                              Robert J. Cresci, General Partner


ACCEPTED:

BROWN BROTHERS HARRIMAN & CO.

By:   /s/ Joseph E. Hall
    ------------------------------
    Joseph E. Hall, Deputy Manager


STATE STREET BANK AND TRUST COMPANY

By:   /s/ Bernie S. Daniels
    ------------------------------
    Name:  Bernie S. Daniels
    Title: VP


BROWN BROTHERS HARRIMAN & CO. AS ADMINISTRATIVE AGENT

By:   /s/ Joseph E. Hall
    ------------------------------
    Joseph E. Hall, Deputy Manager

                                         4
<PAGE>

      The Borrower above named hereby acknowledges notice of the within and
      foregoing subordination and agrees to be bound by all the terms,
      provisions and conditions thereof.

      Witness                            Borrower:



      /s/ Jerry L. Burdick               By:  /s/ Barry D. Plost
      -------------------------               ---------------------------------
                                              Barry D. Plost, Chairman and CEO

                                         5