<PAGE>

EXHIBIT 4.9

                             REVOLVING TERM NOTE


                                                                 APRIL 24, 1998

$10,000,000.00                                            Boston, Massachusetts

      For value received, the undersigned (the "Borrower"), promises to pay to 
Brown Brothers Harriman & Co. ("Lender"), or order, the principal amount of Ten 
Million Dollars and Zero Cents ($10,000,000.00) or such lesser amount as may be 
outstanding under that certain Revolving Loan and Security Agreement, dated of 
even date herewith (the "Loan Agreement"), among the Borrower and each 
subsidiary of the Borrower and Lender, on or before April 24, 2000, with 
interest from the date hereof on the said principal balance from time to time 
outstanding. The aggregate principal balance outstanding shall bear interest 
thereon at a per annum rate equal to three-quarters of one percent (0.75%) 
above the Wall Street Journal Prime Rate (as hereinafter defined), payable 
quarterly in arrears on the 1st business day of each calendar quarter, 
commencing July 1, 1998.

      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 Bank 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 at the Lender's main office 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 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 Lender related hereto; 
provided, however, that the principal balance outstanding shall at no time 
exceed the face amount of the 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 that certain Revolving Loan and Security Agreement, dated of even date 
herewith, among Lender, the undersigned; Avre, Inc., Binary Associates, Inc., 
SeraCare Acquisitions, Inc., BHM Labs, Inc., Sera Care Technology, Inc. and 
Western States Group, Inc.

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

      The Borrower represents to the Lender 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 Lender or any of 
its banking or lending affiliates, or any Lender acting as a participant 
under any loan arrangement between the Lender and the Borrower, any endorser 
or guarantor hereof, and any cash, securities, instruments or other property 
of the undersigned in the 




<PAGE>

possession of the Lender or any of its banking or lending affiliates, or any 
Lender acting as a participant under any loan arrangement between the Lender 
and the Borrower, any endorser or guarantor hereof, whether for safekeeping 
or otherwise, or in transit to or from the Lender or any of its banking or 
lending affiliates or any such participant, or in the possession of any third 
party acting on the Lender's behalf (regardless of the reason the Lender had 
received same or whether the Lender 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 
Lender and may be applied or set off against such liabilities and obligations 
of the undersigned or any endorser or guarantor hereof to the Lender 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 Lender.

      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 Lender and its directors, officers, employees, 
agents and attorneys harmless against any claim brought or threatened against 
the Lender by the Borrower, by any endorser or guarantor, or by any other 
person (as well as from attorneys' reasonable fees and expenses in connection 
therewith) on account of the Lender's relationship with the Borrower or any 
endorser or guarantor hereof (each of which may be defended, compromised, 
settled or pursued by the Lender with counsel of the Lender's selection, but 
at the expense of the Borrower and any endorser and/or guarantor), except for 
any claim arising out of the gross negligence or willful misconduct of the 
Lender.

      The Borrower and each endorser and guarantor of this Note agree to pay, 
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 (4%) 
percent plus the rate provided for herein.  If any payment due under this 
Note is unpaid for 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 5.0% 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 Lender and its 
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 Lender 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 Lender.  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 Lender of the person from whom contribution is sought have been satisfied 
in full.  The release or compromise by the Lender 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 
Lender if marked "copy" or 


                                      2

<PAGE>

"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 Lender 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. 

      The Borrower and each endorser and guarantor of this Note each 
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 Borrower, endorser or 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 
Borrower, endorser or 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 Lender 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 BORROWER, ENDORSER AND GUARANTOR AND LENDER EACH HEREBY KNOWINGLY, 
VOLUNTARILY AND INTENTIONALLY, AND AFTER AN OPPORTUNITY TO CONSULT WITH LEGAL 
COUNSEL, WAIVE ANY AND ALL RIGHTS TO A TRIAL BY JURY IN ANY ACTION OR 
PROCEEDING IN CONNECTION WITH THIS NOTE, ALL OF THE OBLIGATIONS OF EACH 
BORROWER TO THE LENDER, AND ALL MATTERS CONTEMPLATED HEREBY AND DOCUMENTS 
EXECUTED IN CONNECTION HEREWITH.  EACH BORROWER, ENDORSER AND GUARANTOR 
CERTIFIES THAT NEITHER THE LENDER NOR ANY OF ITS REPRESENTATIVES, AGENTS OR 
COUNSEL HAS REPRESENTED, EXPRESSLY OR OTHERWISE, THAT THE LENDER WOULD NOT IN 
THE EVENT OF ANY SUCH PROCEEDING SEEK TO ENFORCE THIS WAIVER OF RIGHT TO 
TRIAL BY JURY.

                             [INTENTIONALLY LEFT BLANK]


                                       3
<PAGE>

      Executed as an instrument under seal as of April 24, 1998.

Witness                              Borrower:

                                     SeraCare, Inc.


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


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




                            STATE OF CALIFORNIA


-------------------, ss.                                    April 24, 1998

      Then personally appeared the above-named Barry D. Plost, Chairman and CEO 
of SeraCare, Inc., and acknowledged the foregoing instrument to be the free act 
and deed of SeraCare, Inc., before me,


                                     /s/                        , Notary Public
                          --------------------------------------

                          My Commission expires: -----------------------------


                                       4