<PAGE>

                                                            EXHIBIT A


                            FOURTH AMENDMENT TO THE
                        AMENDED AND RESTATED EXCLUSIVE
                            DISTRIBUTION AGREEMENT
<PAGE>

                               TABLE OF CONTENTS

<TABLE>
<S>                                                                          <C>
I.   DEFINITIONS...........................................................   2
    1.1  Additional Definitions............................................   2
    1.2  Other Definitions.................................................   9

II.  TERM..................................................................   9
    2.1  Term..............................................................   9
    2.2  Termination.......................................................   9

III. DISTRIBUTION RIGHTS...................................................   9
    3.1  Grant of Distribution Rights......................................   9
    3.2  Distributor Noncompete............................................  10
    3.3  Supplier Exclusivity..............................................  10
    3.4  Hemostasis Point-of-Care Products.................................  11
    3.5  Future Product Discontinuances....................................  11
    3.6  Ordering..........................................................  12

IV.  SUPPLIER DUTIES.......................................................  12
    4.1  Drop Shipments and Purchase of Inventory..........................  12
    4.2  Returned Goods....................................................  13
    4.3  Supplier Modifications to Active AdNow Leases.....................  14
    4.4  Supplier Guarantees...............................................  15
    4.5  Duty to Cooperate.................................................  15

V.   DISTRIBUTOR'S DUTIES..................................................  15
    5.1  BVP Status........................................................  15
    5.2  Stocking Products.................................................  16
    5.3  Returned Goods....................................................  16

VI.  LEASING...............................................................  16
    6.1  Third Party Leasing Agent.........................................  16
    6.2  Certain AdNow Leases..............................................  18
    6.3  Continuing Leasing Obligations....................................  18
    6.4  Leasing on Expiration or Termination..............................  19
    6.5  Lease Variances...................................................  26
    6.6  Supplier Interference; Conversions................................  27
    6.7  Distributor Interference; Conversions.............................  28

VII. PAYMENT TERMS.........................................................  29
    7.1  Guaranteed Gross Profit Margin....................................  29
    7.2  Offsets or Deductions; Expedited Dispute Resolution Process
         Matters...........................................................  29
    7.3  Rebates on Unsold Products........................................  32
    7.4  Supplier Receivables..............................................  33
    7.5  Payments Received.................................................  33
</TABLE>

                                      -i-
<PAGE>

<TABLE>
<S>                                                                          <C>
VIII.   TRANSITION.........................................................  34
 8.1    Transition Payment.................................................  34
 8.2    Assignment of Contracts............................................  34
 8.3    Government Contracts...............................................  34
 8.4    Transition Information.............................................  35
 8.5    Transition Principles..............................................  35

IX.     SURCHARGE REMOVALS.................................................  35
 9.1    Surcharge Removals.................................................  35

X.      VALUE BONDS........................................................  36
 10.1   Retirement of Value Bonds..........................................  36

XI.     EXPEDITED ARBITRATION PROCEDURE....................................  36
 11.1   Arbitration........................................................  36

XII.    MISCELLANEOUS......................................................  38
 12.1   Drafting...........................................................  38
 12.2   Scope of Promises, Representations, and Inducements................  39
 12.3   Voluntary Agreement................................................  39
 12.4   Survival...........................................................  39
 12.5   Governing Law......................................................  39
 12.6   Severability.......................................................  40
 12.7   Entire Agreement...................................................  40
 12.8   Successors and Assigns.............................................  40
 12.9   Modifications......................................................  40
 12.10  Authorization to Sign..............................................  41
 12.11  Counterparts.......................................................  41
 12.12  Headings...........................................................  41
 12.13  Confirmation.......................................................  41
</TABLE>

                                     -ii-
<PAGE>

                                                                    EXHBIIT 10.3

                            FOURTH AMENDMENT TO THE
                        AMENDED AND RESTATED EXCLUSIVE
                            DISTRIBUTION AGREEMENT

     This Fourth Amendment to the Amended and Restated Exclusive Distribution
Agreement ("Fourth Amendment") by and between Dade Behring Inc., ("Supplier")
and Allegiance Healthcare Corporation ("Distributor") is entered into this 9th
day of August, 2000.

     WHEREAS, Supplier and Distributor are parties to that Amended and Restated
Exclusive Distribution Agreement, dated September 15, 1995 (the "Amended and
Restated Distribution Agreement"), as amended by the parties pursuant to the
Amendment to Amended and Restated Exclusive Distribution Agreement, dated as of
September 26, 1996 (the "First Amendment"), the Second Amendment to Amended and
Restated Exclusive Distribution Agreement, dated as of October 1, 1997 (the
"Second Amendment"), the Third Amendment to the Amended and Restated Exclusive
Distribution Agreement, dated as of May 27, 1998 (the "Third Amendment"), that
certain letter agreement, dated March 4, 1999 (the "March Letter Agreement"),
that certain letter agreement dated February 29, 2000 (the "February Letter
Agreement"), and that certain letter agreement, dated April 11, 2000 (the "April
Letter Agreement") (the Amended and Restated Distribution Agreement, as amended
and supplemented pursuant to the foregoing, is hereinafter referred to as the
"Distribution Agreement");

     WHEREAS, disputes have arisen between Supplier and Distributor relating to
the Distribution Agreement some of which are currently the subject of an
arbitration proceeding between the parties pending before Robert A. Helman
("Arbitration");

                                      -1-
<PAGE>

     WHEREAS, the parties have agreed to settle their claims pursuant to the
terms and conditions of the Settlement Agreement, Mutual Release and Covenant
Not to Sue ("Settlement Agreement") among Supplier, Distributor and Baxter
Healthcare Corporation, dated as of the date hereof; and

     WHEREAS, as a part of their settlement the parties have agreed to enter
into this Fourth Amendment, which will be an exhibit to the Settlement
Agreement, and, notwithstanding anything to the contrary contained in the
Settlement Agreement, the parties agree that nothing in the Settlement Agreement
shall negate or otherwise affect any rights or obligations of the parties set
forth herein.

     NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, the parties hereto agree as
follows:

                               I.    DEFINITIONS

     1.1  Additional Definitions.  The following definitions are hereby added to
          ----------------------
Section 1 of the Distribution Agreement:

          "Active AdNow Leases" shall mean those AdNow leases for which the
     original contractual term of the lease has not expired or has not been
     otherwise prematurely terminated by both parties to the lease. The 180
     Columbia/HCA customer contracts will be deemed to be Active AdNow leases
     for purposes of this Agreement.

          "Agency Agreement" shall have the meaning set forth in Section
                                                                 -------
     9(e)(iv).
     --------

                                      -2-
<PAGE>

          "Agreed Arbitrator" shall mean a former federal judge or other
     mutually agreed upon individual who is selected by the parties and agrees
     to hear claims under Section 16(d) of this Agreement arising between the
                          -------------
     parties.

          "Agreed Net Book Value" of an Instrument shall mean, for each
     Instrument subject to an Active AdNow Lease, the Net Book Value multiplied
     by the fraction equal to the portion of the monthly Instrument Surcharge
     added to Supplier's Products as a percentage of the total monthly
     Instrument Surcharge due under such Active AdNow Lease.

          "April Letter Agreement" means that certain letter agreement, dated
     April 11, 2000, between Distributor and Supplier.

          "Conversion" shall have the meaning set forth in Section 6(aa).
                                                           -------------

          "Distributor Loss Pool Amount" shall mean the amount of One Million
     Five Hundred Thousand and no/100 dollars ($1,500,000.00).

          "Distributor Responsibility Reasons" means that a customer's attempted
     termination of its AdNow lease is because of Distributor's breach of any of
     its obligations under such AdNow lease to place orders for Products, to
     ship Products (to the extent such shipping is, at that time, a Distributor
     duty rather than a Supplier duty under the terms of this Agreement or the
     April Letter Agreement) or to bill the customer.

                                      -3-
<PAGE>

          "Dual Responsibility Reasons" means that a customer's attempted
     termination of its AdNow lease is for any reason other than a Distributor
     Responsibility Reason or a Supplier Responsibility Reason.

          "Event of Default" shall mean (i) a failure by Supplier to remit any
     Monthly Instrument Collections pursuant to the Agency Agreement, or any
     Monthly Instrument Shortfall Payment; provided that Distributor has given
                                           --------
     Supplier notice of such failure and Supplier has failed to remit such
     payment within five business days from the date of such notice, (ii) any
     breach by Supplier of any of its obligations under the Agency Agreement;
     provided that Distributor has given Supplier notice of such failure and
     --------
     Supplier has failed to cure such breach within fifteen (15) days of such
     notice, or (iii) Supplier is Insolvent, fails to operate as a going
     concern, files or has filed against it a petition in bankruptcy, makes an
     assignment for the benefit of creditors, has a receiver appointed for it or
     dissolves.

          "Expedited Dispute Resolution Process" shall mean that process set out
     in Section 16(d) of this Agreement.
        -------------

          "February Letter Agreement" means that certain letter agreement, dated
     February 29, 2000, between Distributor and Supplier.

          "Insolvent" or "Insolvency" shall mean that an individual or entity
     cannot pay his, her or its debts as they become due.

                                      -4-
<PAGE>

          "Instrument of Assignment" shall have the meaning set forth in Section
                                                                         -------
     9(e)(i).
     -------

          "Instrument of Assumption" shall have the meaning set forth in Section
                                                                         -------
     9(e)(i).
     -------

          "Instrument Portion" shall have the meaning set forth in Section
                                                                   -------
     9(e)(i).
     -------

          "Instrument Surcharge" shall mean that aggregate portion of the
     reagent or consumable prices allocable to the Instrument together with the
     Instrument service fees (if financed by Distributor) and the Instrument
     financing charges applicable to an AdNow lease and calculated by
     Distributor utilizing methodology consistent with Exhibit C to the Second
     Amendment (whether or not the lease was entered into after October 1, 1997)
     and once set for a particular AdNow lease it shall remain the same for the
     term of such AdNow lease.

          "March Letter Agreement" means that certain letter agreement, dated
     March 4, 1999, between Distributor and Supplier.

          "Monthly Instrument Collections" shall have the meaning set forth in
     Section 9(e)(v).
     ---------------

          "Monthly Instrument Payment" shall equal the Agreed Net Book Value of
     the Instrument(s)  subject to an Active AdNow Lease together with the
     Instrument

                                      -5-
<PAGE>

     financing charges applicable to such lease, divided by the number of months
     remaining in the original term of the Active AdNow Lease.

          "Monthly Instrument Shortfall Payment" shall have the meaning set
     forth in Section 9(e)(v).
              ---------------

          "Net Book Value" of an Instrument shall mean the unamortized value of
     the Instrument plus Instrument service fees (if financed by Distributor)
     utilizing the "effective interest method" of amortization.

          "Net Purchase Price" shall mean the price charged to Distributor by
     Supplier for the Saleable Inventory offset by any amounts that Distributor
     owes to Supplier but has not yet paid to Supplier for such Saleable
     Inventory as of the date Supplier pays Distributor for such Saleable
     Inventory.

          "Return Process" shall mean the following process under which
     Distributor returns Saleable Inventory to Supplier:  On the dates set forth
     in Section 6(a)(2) hereof, Distributor shall begin the process of returning
        ---------------
     the applicable Saleable Inventory to Supplier. Distributor will have two
     (2) weeks from either January 31, 2001, or March 31, 2001, respectively, to
     complete the shipment of the Saleable Inventory to Supplier's designated
     distribution centers. Distributor shall ship such Saleable Inventory in
     accordance with Supplier's shipping instructions (FOB destination).
     Thereafter, Supplier shall have two (2) weeks to reconcile and accept or
     reject such inventory. Supplier shall assume responsibility for any loss,
     damage

                                      -6-
<PAGE>

     (including from improper storage) or destruction of such Products which
     occurs on or after Supplier's receipt of such Products at its warehouse
     dock. Title to all Products included within the Saleable Inventory will
     pass to Supplier upon Supplier's acceptance of such Products.

          "Saleable Inventory" shall mean Distributor's entire inventory of
     Products except Products that are obsolete, have less than 90 days
     remaining shelf life, are not in good resaleable condition or are not in
     their original packaging.

          "Settlement Agreement" means that Settlement Agreement, Mutual Release
     and Covenant Not to Sue, dated August 9, 2000, among Distributor, Supplier
     and Baxter Healthcare Corporation.

          "Supplier Responsibility Reasons" means that a customer's attempted
     termination of its AdNow lease is because of (i) a breach of Supplier's
     warranty, (ii) Supplier's failure to ship Products in accordance with the
     terms and conditions hereof to the customer (to the extent such shipping
     is, at that time, a Supplier duty rather than a Distributor duty under the
     terms of this Agreement or the April Letter Agreement) or (iii) Supplier's
     failure to supply Products to Distributor in accordance with the terms and
     conditions hereof.

          "Third Party Transaction" shall have the meaning set forth in Section
                                                                        -------
     13(k).
     -----

                                      -7-
<PAGE>

          "Valid Active AdNow Leases" shall mean all Active AdNow Leases as of a
     specified date, other than those (i) for which a signed lease form does not
     exist; (ii) with customers who are bankrupt or Insolvent; (iii) for which
     the Instrument(s) cannot be physically located; (iv) for which Distributor
     (or Supplier at Distributor's request) has removed the Instrument(s) from
     the customer's location; and (v) for which (A) Distributor has actually
     received a written notice of termination from the customer, (B) the
     customer is attempting to terminate because of a Distributor Responsibility
     Reason and (C) Distributor has not cured or taken reasonable steps to cure
     such breach. Notwithstanding the above, the 180 Columbia/HCA customer
     contracts will be deemed to be "Valid Active AdNow Leases," other than
     those for which Distributor has removed the Instrument(s) from the
     customer's location.

          "Valid Inactive AdNow Leases" shall mean all AdNow leases as of a
     specified date that would be Valid Active AdNow Leases but for the fact
     that the original contractual term of the lease has expired (provided that
     such AdNow lease is in its renewal term), other than such AdNow leases
     which cover any non-Supplier products.

          "Value Bonds" is used herein as such term is used in the Purchase
     Agreement, as amended and restated as of December 15, 1994, between
     Diagnostics Holding, Inc. (n/k/a Dade Behring Holdings, Inc.) and Baxter
     International Inc.

                                      -8-
<PAGE>

     1.2  Other Definitions.  All other capitalized terms used but not defined
          -----------------
herein shall have the meanings ascribed to them in the Distribution Agreement.


                                  II.    TERM


     2.1  Term.  The first sentence of Section 3 of the Distribution Agreement
          ----
is hereby amended to read as follows:

     The term of this Agreement shall begin on the date of this Agreement and
     shall end on June 30, 2001, unless sooner terminated as provided herein.

     2.2  Termination.  (a) The first two clauses of Section 8(c) of the
          ------------
Distribution Agreement are hereby amended to read as follows:

     At any time on or after September 30, 2000 for the MicroScan class of
     Products and at any time on or after December 31, 2000 for the Hemostasis
     class of Products, Supplier may terminate this Agreement upon at least six
     months prior written notice, [Section 8(c) then continues: "if the
     business...."]

     (b)  Section 8(d) of the Distribution Agreement is hereby amended to read
in its entirety as follows:

     INTENTIONALLY DELETED


                          III.    DISTRIBUTION RIGHTS


     3.1  Grant of Distribution Rights.  The first clause of Section 2(a)(1) of
          -----------------------------
the Distribution Agreement is hereby amended to read in its  entirety as
follows:

     Except as otherwise specifically set forth herein, Supplier will distribute
     (i) the Hemostasis class of Products exclusively through Distributor during
     the Term of this Agreement, (ii) the MicroScan class of Products
     exclusively through Distributor through March 31, 2001 and thereafter
     through Distributor during the remaining Term of this Agreement on a non-
     exclusive basis, and (iii) the Dade

                                      -9-
<PAGE>

     Immunohematology and Other Dade classes of Products non-exclusively through
     Distributor during the Term of this Agreement; [Section 2(a) then
     continues: "provided, however, that nothing in...."]
                 --------- -------

     3.2  Distributor Noncompete.  Subsections 2(b)(1)(i) through (iv) of the
          -----------------------
Distribution Agreement are hereby amended to read in their entirety as follows:

     (i) manufacture, sell, lease, solicit orders for or otherwise distribute in
     the Territory any product that is competitive with any Product in either
     the MicroScan or Hemostasis classes of Products while Supplier is
     distributing any such MicroScan or Hemostasis Product exclusively through
     Distributor pursuant to Section 2(a)(1) of this Agreement; or (ii) operate,
                             ---------------
     manage, advise or otherwise assist in any manner (in each case, either
     alone or in association with any other person) in the manufacture, leasing
     or sale within the Territory of products that are competitive with any
     Product in either the MicroScan or Hemostasis classes of Products while
     Supplier is distributing any such Product exclusively through Distributor
     pursuant to Section 2(a)(1) of this Agreement; (iii) purchase more than a
                 ---------------
     ten percent (10%) interest in a company whose annual gross revenues from
     the manufacture, lease or sale in the Territory of products competitive
     with Products in the Hemostasis class of Products (or, until March 31,
     2001, the MicroScan class of Products) exceeds fifty million dollars
     ($50,000,000); or (iv) own more than a ten percent (10%) equity interest in
     a company whose annual gross revenues from the manufacture, lease or sale
     in the Territory of products competitive with Products in the Hemostasis
     class of Products (or, until March 31, 2001, the MicroScan class of
     Products) exceeds an amount equal to fifty million dollars ($50,000,000)
     times a fraction (A) the numerator of which is the value of the consumer
     price index for medical products in effect on the most recent month for
     which such index is available at the time of the acquisition of such
     interest and (B) the denominator of which is the value of such index as of
     December 14, 1994.

     3.3  Supplier Exclusivity.  Section 2(a)(2) of the Distribution Agreement
          --------------------
is hereby amended to add the following to the end thereof:

     Supplier shall not be deemed to have breached Section 2(a)(1) of this
                                                   ---------------
     Agreement for any sale, solicitation of orders for, or other distribution
     of, Products within the Territory other than through Distributor where (i)
     Distributor has been deemed to have consented to such actions pursuant to
     the terms of Section 2 of the Amendment (otherwise known as the First
     Amendment) to this Agreement, (ii) Supplier has assisted a customer in
     financing an Instrument through a third party leasing agent and the third
     party leasing agent has leased the Instrument to such customer, pursuant to
     the terms of the February Letter Agreement or the terms of

                                      -10-
<PAGE>

     Section 6(d) of this Agreement (including in each case that all reagents
     -----------
     and consumables under such lease are sold through Distributor and
     Distributor receives its guaranteed gross profit margins provided in this
     Agreement from such sale or lease of Products (including all Instruments,
     consumables and reagents) that are subject to such lease until the
     expiration or termination of this Agreement), (iii) Supplier has exercised
     its rights under Section 2(d) of this Agreement or (iv) Distributor has
     otherwise consented in writing to such sale or solicitation of orders for
     or other distribution of Products within the Territory.

     3.4  Hemostasis Point-of-Care Products. (a) Subpart (x) of the second
          ---------------------------------

sentence of Section 2(b)(1) of the Distribution Agreement is hereby amended to
read in its entirety as follows:

     nothing in this Agreement shall prohibit Distributor or any of its
     Affiliates from selling, soliciting orders for or otherwise distributing
     the products referred to on Exhibit C hereto, which are competitive with
                                 ---------
     the Products; and

     (b)  Exhibit C to the Distribution Agreement is hereby amended to add the

following to the end thereof:

     24.  Hemostasis Point-of-Care Products (which means coagulation diagnostic
     instruments as are typically hand-held/mobile and test one sample at a
     time; they (i) may be used at a hospital bedside, in a residence or in a
     physician's office and (ii) are not intended to compete directly, by way of
     features or price, with coagulation diagnostic instruments incorporating
     automated reagent delivery and specimen sampling systems).

     (c)  Section 2(a)(1) of the Distribution Agreement is hereby amended to add
the following as the final sentence thereof:

     In the event that Distributor is selling, soliciting orders for or
     otherwise distributing competitive Hemostasis Point-of-Care Products, then
     Supplier may sell, solicit orders for or otherwise distribute Hemostasis
     Point-of-Care Products other than through Distributor.

     3.5  Future Product Discontinuances. The second sentence of Section 2(c) of
          ------------------------------

the Distribution Agreement is amended to add the following proviso to the end
thereof:

                                      -11-
<PAGE>

     ; provided, however, if Supplier does discontinue the manufacture and sale
       --------  -------
     of a Product after the effective date of the Fourth Amendment to this
     Agreement and either (i) no commercially reasonable substitute for such
     Product is then being sold by Supplier to Distributor (a commercially
     reasonable substitute shall be any similar Product sold by Supplier to
     Distributor that can substitute for such discontinued Product or another
     Supplier Product which a customer agrees may be added to its Active AdNow
     Lease to cover the discontinued Product's portion of the Instrument
     Surcharge), or (ii) a customer does not agree to a price increase on the
     remaining Products subject to its Active AdNow Lease to cover the
     discontinued Product's portion of the Instrument Surcharge, then for any
     such discontinued Product, in each case, Supplier shall pay to Distributor
     the portion of any net behind lease variance which accrues on each Active
     AdNow Lease after the date of the Fourth Amendment to this Agreement which
     is directly attributable to the Product discontinuance (it being understood
     by the parties that this Section is not applicable with respect to Products
     that Supplier no longer manufactures or sells because the business to which
     those Products belong is sold).

     3.6  Ordering. Section 2(i) of the Distribution Agreement is hereby amended
          --------

to read in its entirety as follows:


     INTENTIONALLY OMITTED

                            IV.    SUPPLIER DUTIES

     4.1  Drop Shipments and Purchase of Inventory. Section 6(a)(2) of
          ----------------------------------------

Distribution Agreement is hereby amended by adding the following to the end
thereof:

     For all orders received by Distributor after January 1, 2001, Supplier
     shall drop ship, on behalf of Distributor, Products to Distributor's
     customers in accordance with instructions received from Distributor;
     provided, however, notwithstanding the January 1, 2001 date, Distributor
     --------  -------
     shall continue to ship Products pursuant to customer orders until it has
     depleted its inventory of such Products. Supplier agrees to drop ship such
     Products on a timely basis, based on the information provided by
     Distributor to Supplier. Supplier shall insure, at its own expense, all
     Products shipped to customers for the invoice price to the customer less
     the guaranteed gross profit margin due to Distributor for such Products and
     shall handle any claims made against such insurance directly with the
     insurer on behalf of Distributor. Notwithstanding anything to the contrary
     contained herein, Supplier shall continue to drop ship all programs of
     Hemostasis single lot reagents and QAP controls which began on or after May
     1, 2000, to Distributor's

                                      -12-
<PAGE>

     customers throughout the term of this Agreement pursuant to the April
     Letter Agreement. Prior to January 1, 2001, Distributor shall continue to
     order and stock all MicroScan Products and the non-single lot Hemostasis
     reagents and non-QAP Hemostasis controls in accordance with Section 5(h) of
                                                                 -----------
     this Agreement. On and after January 1, 2001, Supplier shall use its
     commercially reasonable efforts to cause its manufacturing sites not to
     accept or fill any further orders from Distributor for any Products unless
     such orders are reviewed and authorized by Distributor's Vice President of
     Operations. Notwithstanding any of the foregoing, Distributor and Supplier
     agree that in the event that Distributor has not depleted its inventory of
     MicroScan Products by January 31, 2001, or its inventory of Hemostasis and
     Other Dade Products by March 31, 2001, then, on the applicable date,
     Distributor shall initiate the Return Process for all of Distributor's
     MicroScan, Hemostasis and Other Dade Saleable Inventory. Distributor and
     Supplier agree to execute the Return Process pursuant to the terms thereof.
     Upon shipment of such Saleable Inventory by Distributor to Supplier,
     Distributor shall invoice Supplier for such Saleable Inventory, and
     Supplier shall pay that portion of the Net Purchase Price of the Saleable
     Inventory which is not disputed on net 60 day terms.

     4.2  Returned Goods.  The first two sentences of Section 6(h) of the
          ---------------

Distribution Agreement are hereby deleted and replaced with the following:

     Accept the return of an Instrument: (i) from a customer, provided Supplier
     has approved (a) any such return, and (b) the amount of Distributor's
     credit to such customer in advance; (ii) from Distributor in a case where
     Distributor has leased an Instrument to a customer, the customer has
     defaulted on the Active AdNow Lease as a result of its bankruptcy, the
     bankruptcy has occurred after the effective date of the Fourth Amendment to
     this Agreement and, in the case of a customer's Chapter 11 bankruptcy, the
     customer has also rejected the lease under (S)365 of the Bankruptcy Code
     (bankruptcy shall mean the voluntary or involuntary filing of a petition
     under the United States Bankruptcy Code by or against such customer); and
     (iii) from Distributor in a case where Distributor has leased an Instrument
     to a customer, the customer has defaulted on the Active AdNow Lease as a
     result of its Insolvency, the Insolvency has occurred after the effective
     date of the Fourth Amendment to this Agreement and Distributor has made a
     good faith effort to enforce its lease. In the case of clauses (ii) and
     (iii), Distributor shall repossess the Instrument from the customer or
     shall request, in writing, that Supplier repossess the Instrument from the
     customer and upon such request, Supplier shall be obligated to repossess
     the Instrument as Distributor's agent (at Distributor's sole cost, which
     cost shall be commercially reasonable). With respect to returns on account
     of a customer's bankruptcy or Insolvency, Supplier shall pay to Distributor
     (a) an amount equal to the Net Book Value of the Instrument (in the case of
     a bankruptcy or Insolvency the Net Book Value shall be calculated at the

                                      -13-
<PAGE>

     time the customer stops paying Distributor) minus any sums which
     Distributor receives from time to time from such customer in payment of
     such Net Book Value (including but not limited to amounts received from a
     proof of claim or from collection efforts) and (b) an amount equal to all
     sums which Distributor has paid to Supplier and which have not been paid to
     Distributor by the customer, for Instrument service fees (irrespective of
     whether any portion of such Instrument service fees were paid by
     Distributor prior to the date of the Fourth Amendment hereto). For purposes
     of the preceding sentence, any sums received from time to time from such
     customer after the date as of which the Net Book Value of the Instrument is
     calculated shall be applied toward the outstanding Net Book Value on the
     one hand and toward other outstanding amounts owed to Distributor on the
     other hand, in the same proportions as such outstanding Net Book Value
     amount and such other outstanding amounts relate to the entire amount owed
     by such customer to Distributor. Distributor shall also be entitled to such
     payment whenever Supplier waives or has waived, in writing, the return of
     the Instrument, which waiver shall not be unreasonably withheld; provided,
                                                                      --------
     however, in a case where the customer cannot be found or the Instrument
     -------
     cannot be found, Supplier shall only reimburse Distributor an amount equal
     to the amount of the Instrument service fees paid to Supplier since the
     Fourth Amendment to this Agreement by Distributor but which have not been
     paid to Distributor by the customer on such Active AdNow Lease, calculated
     as of the date set forth above. Notwithstanding anything in the Settlement
     Agreement or this Agreement to the contrary, Supplier agrees to accept the
     return of an Instrument from Distributor and to pay to Distributor the
     above-described Net Book Value (plus any relevant Instrument service fees)
     for any Instrument which Distributor repossesses (or requests Supplier to
     repossess for it) from a customer, on account of such customer's
     bankruptcy, when the bankruptcy occurs after the effective date of the
     Fourth Amendment to this Agreement but when the customer's Insolvency
     occurred prior to the effective date of the Fourth Amendment to this
     Agreement. Notwithstanding the foregoing, Supplier shall not be obligated
     to accept the return of any Instrument from Distributor or pay Distributor
     for the Net Book Value of any Instrument where Distributor did not notify
     Supplier, in writing, of the bankruptcy or Insolvency within twelve (12)
     months after the customer's bankruptcy or Insolvency; provided that this
                                                           --------
     exception does not apply where Supplier has taken possession of the
     Instrument. [Section 6(h) then continues: "The Instrument will then...."]

     4.3  Supplier Modifications to Active AdNow Leases.  Section 6 of the
          ----------------------------------------------

Distribution Agreement is hereby amended to add the following as a new
subsection (w) thereof:

     Notwithstanding any other provision of this Agreement, the Fourth Amendment
     hereto or the Settlement Agreement, in the event that Supplier's employees
     or agents, after the date of the Fourth Amendment to this Agreement, enter
     into a

                                      -14-
<PAGE>

     written agreement or side letter with a customer that purports to alter or
     modify the terms or conditions of an Active AdNow Lease, and as a direct
     result of such agreement or side letter, Distributor suffers any losses,
     damages, claims, costs or expenses (such as net behind lease variances,
     unpaid Net Book Value on the Instrument(s) or unpaid accounts receivable),
     Supplier shall pay to Distributor the amount of such actual losses,
     damages, claims, costs or expenses (but in no event shall Supplier be
     liable for any incidental or consequential damages, costs or expenses
     incurred by Distributor as a result of such agreement or side letter). Upon
     such payment by Supplier to Distributor, the customer's Active AdNow Lease
     will be deemed to be altered or modified in the manner specified in such
     written agreement or side letter between Supplier and such customer.

     4.4  Supplier Guarantees. Section 6 of the Distribution Agreement is hereby
          -------------------
amended to add the following as a new subsection (x) thereof:

     In the event that on or after December 1, 1999, Supplier guarantees or has
     guaranteed in writing, all or part of a customer's payment or other
     obligations under an AdNow lease or indemnifies or has indemnified, in
     writing, Distributor against losses resulting from any default by such
     customer and, in any such case, the customer defaults on any of its
     obligations to Distributor under such AdNow lease so guaranteed or
     indemnified against, Supplier agrees to pay to Distributor the amount
     guaranteed or indemnified against by Supplier (irrespective of whether the
     default occurred or any portion of such amount was due prior to the date of
     the Fourth Amendment hereto).

     4.5  Duty to Cooperate.  Section 6 of the Distribution Agreement is hereby
          ------------------

amended to add the following as a new subsection (y) thereof:

     Supplier agrees to provide to Distributor reasonable assistance with
     Distributor's resolution of customer disputes relating to Products,
     including but not limited to any alleged deficiency in the performance of
     an Instrument, delays in installation or service of an Instrument,
     overstatement of the reagent usage for an Instrument, and unavailability of
     reagents used with an Instrument.


                            V. DISTRIBUTOR'S DUTIES


     5.1  BVP Status. Section 5(1) of the Distribution Agreement is hereby
          ----------
amended in its entirety to read as follows:

                                      -15-
<PAGE>

     Distributor represents that its current and most favorable incentive
     compensation program is the Best Value Program. Regardless of whether or
     not Supplier or the Products meet the definition of Best Value Products,
     Distributor shall promote the Hemostasis and MicroScan classes of Products
     as the only Best Value Products for these or similar types of products
     during the Term of this Agreement. In the event Distributor creates a new
     promotion or incentive program in addition to or in substitution of its
     Best Value Program, such Hemostasis and MicroScan Products shall be granted
     the most favorable treatment under such new promotion or incentive program,
     regardless of whether Supplier or such Products meet the criteria for such
     treatment, for the time periods set forth above. In the event that
     Distributor generally discontinues its incentive compensation programs,
     Distributor agrees to offer an incentive compensation program featuring
     such Products for the Term of this Agreement.

     5.2  Stocking Products. The first sentence of Section 5(h) of the
          -----------------

Distribution Agreement is hereby amended to add the following proviso to the end
thereof:

     ; provided, however, that effective on January 1, 2001, any duty
       --------  -------
     Distributor may have to stock any Product (other than remaining inventory)
     shall terminate.

     5.3  Returned Goods. The second sentence of Section 5(j) of the
          --------------

Distribution Agreement is hereby amended to add the following to the beginning
thereof:

     Except as provided in Section 6(h) of this Agreement, [Section 5(j) then
                           ------------
     continues:  "Distributor shall not...."]


                                  VI. LEASING


     6.1  Third Party Leasing Agent. Section 13 of the Distribution Agreement is
          -------------------------

hereby amended to add the following as a new subsection (k) thereof:

     The parties agree to use commercially reasonable efforts to obtain a
     written offer from one third party leasing agent of Supplier's choice and
     one third party leasing agent of Distributor's choice to purchase the
     Instruments subject to those AdNow leases that are then-outstanding Active
     AdNow Leases (including all other financed equipment that interface with
     such Instruments ("Leased Instruments")), the Instrument Portion of each
     such Active AdNow Lease and/or the lease receivables relating to such
     Leased Instruments (the "Third Party Transaction") by

                                      -16-
<PAGE>

     October 31, 2000. Either Distributor or Supplier may reject any offer
     relating to a Third Party Transaction or the terms of any such transaction
     in such party's sole discretion. In the event the parties mutually agree to
     accept an offer relating to a Third Party Transaction, Distributor and
     Supplier agree that the terms of such Third Party Transaction will include
     the following, unless otherwise agreed in writing by the parties: (i)
     Distributor shall pay, in cash, on the date such Third Party Transaction is
     consummated to such third party leasing agent and/or Supplier a total of
     $1.5 million for all potential recourse against Distributor in connection
     with the Leased Instrument portfolio (subject to the next two sentences),
     and (ii) any additional recourse required by the third party leasing agent
     in excess of such payment made by Distributor shall be Supplier's sole
     obligation and responsibility. It is understood that after the $1.5 million
     payment specified above is made, neither the third party leasing agent nor
     Supplier shall have any recourse against Distributor for any claims,
     liabilities, damages, losses or expenses relating to the Leased Instrument
     portfolio included in the Third Party Transaction (including claims
     relating to any amounts unpaid by customers under, or claims relating to,
     any AdNow lease assigned to such third party leasing agent), other than (A)
     amounts owed by Distributor for personal property taxes on the Instruments
     which are assessed for the period prior to the consummation of the Third
     Party Transaction, and (B) losses which are incurred by Supplier or such
     third party leasing agent as a direct result of either Distributor's
     failure to file any UCC financing statement or Distributor's failure to
     insure any of the Instruments. Notwithstanding the foregoing, in the event
     the third party leasing agent demands recourse for any additional event
     that is primarily within Distributor's control, Distributor and Supplier
     agree to negotiate in good faith to resolve such additional recourse
     issues.

     In the event that such third party leasing agent declines to purchase any
     Valid Active AdNow Lease for which (A) Distributor has actually received a
     written notice of termination from the customer, (B) the customer is
     attempting to terminate because of any Supplier Responsibility Reason or
     Dual Responsibility Reason and (C) such breach or failure has not been
     cured nor have reasonable steps been taken to cure such breach or failure,
     then at the time the Third Party Transaction is consummated Supplier shall
     pay to Distributor (x) in cases of attempted termination because of any
     Supplier Responsibility Reason, the Agreed Net Book Value of the
     Instrument(s) subject to that AdNow lease, and (y) in cases of attempted
     termination because of any Dual Responsibility Reason, 50% of the Agreed
     Net Book Value of the Instrument(s) subject to that AdNow lease. After
     Distributor's receipt from Supplier of the Agreed Net Book Value pursuant
     to subsection (x) above and upon Supplier's request, Distributor will
     assign to Supplier all of its right, title and interest in such
     Instrument(s).

                                      -17-
<PAGE>

     6.2  Certain AdNow Leases. Section 13 of the Distribution Agreement is
          --------------------

hereby amended to add the following as a new subsection (l) thereof:

     The parties agree to cooperate with each other to modify or amend any AdNow
     lease that is within its original term or any renewal term and which
     includes Supplier's Products and non-Supplier products, so that such AdNow
     leases relate solely to Supplier's Products, in each case to the extent
     permitted by the affected customer(s). To the extent the parties are unable
     to modify any such AdNow leases as provided above, each such unmodified
     AdNow lease will be handled under the provisions of Section 9(e) to the
                                                         ------------
     extent permissible under such AdNow lease and, if not permissible, then
     under the provisions of Section 9(b).
                             ------------

     6.3  Continuing Leasing Obligations.
          -------------------------------

     (a)  Section 5(e)(12) of the Distribution Agreement is hereby amended to

read in its entirety as follows:

     Unless and until Distributor, Supplier and a mutually-agreeable third party
     leasing agent consummate a Third Party Transaction pursuant to Section
                                                                    -------
     13(k), Distributor shall continue to provide leasing services to customers
     -----
     for Supplier's Instruments pursuant to the terms and conditions set forth
     in the Second Amendment and Exhibit C to the Second Amendment to this
     Agreement (except as otherwise provided therein), as amended by the March
     Letter Agreement and the February Letter Agreement, and otherwise pursuant
     to the terms and conditions of the February Letter Agreement and the March
     Letter Agreement.

     (b)  Section 8(a) of the Second Amendment is hereby amended to read in its

     entirety as follows:

     INTENTIONALLY DELETED.

     (c)  Section 6 of the Distribution Agreement is hereby amended to add the

following as a new subsection (z) thereof:

     Supplier's obligations relating to net behind lease variances and the
     Supplier Loss Pools under Exhibit C to the Second Amendment to this
     Agreement shall continue beyond the date of the Fourth Amendment to this
     Agreement including, without

                                      -18-
<PAGE>

     limitation, obligations, if any, relating to customers who are non-
     compliant under the terms of their AdNow leases as of the date of the
     Fourth Amendment to this Agreement (except that all behind lease variances
     or any other amounts for which Supplier may be responsible under such
     Exhibit C and all ahead lease variances incurred or arising prior to the
     Fourth Amendment to this Agreement, unless otherwise provided in such
     Fourth Amendment or the Settlement Agreement, are released under the
     Settlement Agreement). Nothing in the Settlement Agreement or the Fourth
     Amendment to this Agreement shall reduce the amount available in any
     Supplier Loss Pool (as defined in Exhibit C to the Second Amendment to this
     Agreement). Distributor acknowledges that, after the consummation of a
     Third Party Transaction or the assignment to Supplier of the reagent or
     consumable portion of Valid Active AdNow Leases and Valid Inactive AdNow
     Leases pursuant to the terms of Section 9(e)(i), Distributor will no longer
                                     --------------
     have any right to claim funds from the Supplier Loss Pools for the AdNow
     leases subject to such Third Party Transaction or assignment; provided that
                                                                   --------
     on and after the effective date of any termination of the Agency Agreement
     Distributor's right to claim funds from the Supplier Loss Pools will be
     reinstated for such AdNow leases although Distributor may only claim funds
     from the Supplier Loss Pools after the funds in the escrow account
     established pursuant to Section 9(e)(vi) have been fully depleted.
                             ---------------

     6.4  Leasing on Expiration or Termination.
          -------------------------------------

     (a)  Section 9(b) of the Distribution Agreement is hereby amended to read

in its entirety as follows:

     With respect to any AdNow lease that is within its original term or any
     renewal term and is held by Distributor as of the date of the expiration or
     termination of this Agreement, the reagents or consumables portion of which
     has not been assigned to Supplier pursuant to the terms of Section 9(e) of
                                                                -------------
     this Agreement, Supplier shall continue to sell Products to Distributor,
     pursuant to the terms of this Agreement set forth on Schedule 1 to the
                                                          ----------
     Fourth Amendment to this Agreement, and with respect to prices in
     accordance with the terms of this Agreement and agreements with customers,
     to enable Distributor to supply Products under all such agreements with
     customers, until such time as the reagent or consumable portion of the
     AdNow lease is assigned to Supplier pursuant to the terms of Section 9(e)
                                                                  ------------
     of this Agreement (but subject to the provisions of Section 9(e)(iv)
                                                         ----------------
     hereof), or any net behind lease variance and Net Book Value which exists
     on such AdNow lease is fully satisfied, but in no event shall Supplier's
     obligation to supply Product with respect to an AdNow lease extend longer
     than 9 months beyond the original contractual term of such lease.

                                      -19-
<PAGE>

     (b)  Section 9 of the Distribution Agreement is hereby amended to add the
following as a new subsection (e) thereof:

     In the event that Distributor, Supplier and a mutually agreeable third
     party leasing agent have not reached agreement on a Third Party Transaction
     under Section 13(k) of this Agreement, Supplier and Distributor agree that
           -------------
     on or before January 1, 2001, they will begin to jointly identify the Valid
     Active AdNow Leases. In the event that the parties cannot themselves agree
     on which AdNow leases are Valid Active AdNow Leases, then the parties shall
     appoint a mutually agreed-upon independent third party to identify the
     Valid Active AdNow Leases, whose fees shall be shared equally by
     Distributor and Supplier and whose determination in terms of process and
     result shall be binding. Distributor and Supplier agree to use commercially
     reasonable efforts to conclude such identification process on or before May
     31, 2001. Upon the expiration or termination of this Agreement, the
     following terms and conditions shall apply to each AdNow lease that is a
     Valid Active AdNow Lease (and to each Valid Inactive AdNow Lease, to the
     extent specified herein) at such time:

          (i)  Effective upon the expiration or termination of this Agreement
     (irrespective of whether a Third Party Transaction has been consummated),
     Distributor shall assign to Supplier (to the extent permitted thereunder or
     permitted by such customer), and Supplier shall accept such assignment from
     Distributor of, that portion of each AdNow lease that is either a Valid
     Active AdNow Lease or a Valid Inactive AdNow Lease at the time of the
     expiration or termination of this Agreement that relates to Supplier's
     reagents or consumables and Supplier shall assume all liabilities and
     obligations related thereto (including, if a Third Party Transaction has
     been consummated, those obligations owed by Distributor to any third party
     leasing agent with respect to the billing, collecting and other
     administration of any AdNow leases which occur or arise after the date of
     such assignment). Neither Supplier nor Distributor shall be entitled to any
     compensation from the other to effect the assignment and assumption of any
     portion of any AdNow lease. Distributor agrees to execute an instrument of
     assignment, in form and substance reasonably acceptable to Supplier (the
     "Instrument of Assignment"), pursuant to which Distributor shall (A) effect
     the assignment of the portion of the AdNow leases described herein relating
     to Supplier's reagents or consumables and (B) agree to indemnify and hold
     harmless Supplier, its Affiliates and their respective successors, assigns,
     directors, officers and employees with respect to all claims, liabilities,
     damages, losses and expenses, including reasonable attorney's fees caused
     by any failure of Distributor to perform its obligations under such
     Instrument of Assignment. Supplier agrees to execute an instrument of
     assumption, in form and substance reasonably acceptable to Distributor (the
     "Instrument of Assumption"), pursuant to which Supplier shall (A) assume
     all liabilities and obligations of Distributor under the portion of the
     AdNow leases described herein relating to Supplier's reagents or
     consumables (including, if

                                      -20-
<PAGE>

     a Third Party Transaction has been consummated, those obligations owed by
     Distributor to any third party leasing agent with respect to the billing,
     collecting and other administration of any AdNow leases which occur or
     arise after the date of such assignment) and (B) agree to indemnify and
     hold harmless Distributor, its Affiliates and their respective successors,
     assigns, directors, officers and employees with respect to all claims,
     liabilities, damages, losses and expenses, including reasonable attorney's
     fees, caused by any failure of Supplier to perform its obligations under
     such Instrument of Assumption. Distributor and Supplier agree to use
     commercially reasonable efforts to effect such assignment and assumption on
     or as promptly as possible after the date of the expiration or termination
     of this Agreement. It is the intention of Supplier and Distributor that,
     unless a Third Party Transaction has been consummated (in which case
     Section 13(k) and the terms of such Third Party Transaction apply), after
     -------------
     the expiration or termination of this Agreement and notwithstanding the
     appointment of Supplier as collection agent under the Agency Agreement,
     Distributor shall continue to own (i) the Instruments that are subject to
     the Valid Active AdNow Leases and the Valid Inactive AdNow Leases, (ii) the
     portion of each Valid Active AdNow Lease and Valid Inactive AdNow Lease
     that relates to such Instruments (such portion, as further described below,
     the "Instrument Portion"), and (iii) the cash and noncash proceeds thereof.
     Supplier acknowledges that, irrespective of whether or not a Third Party
     Transaction has been consummated, it has and will have no interest in
     either the Instruments that are subject to the Valid Active AdNow Leases or
     the Valid Inactive AdNow Leases or the Instrument Portion of any Valid
     Active AdNow Lease or Valid Inactive AdNow Lease until such time, if any,
     that any such Instrument or Instrument Portion is purchased by, or assigned
     to, Supplier.

               The Instrument Portion of any Valid Active AdNow Lease or Valid
     Inactive AdNow Lease shall include, but not be limited to, (i) the right to
     bill and collect the Instrument Surcharge and late charges and interest on
     any overdue Instrument Surcharge payments; (ii) the right to enforce the
     customer's obligation to pay any applicable taxes and registration fees;
     (iii) the provisions relating to the ownership of the Instrument, including
     the right to require a customer to sign informational UCC filings and the
     like and the benefit of any security interest granted in the Instrument(s);
     (iv) the right to inspect the Instrument(s); (v) the right to receive
     payment for the Instrument(s) at the expiration of the lease; (vi) the
     benefit of any disclaimer of warranties; (vii) the benefit of any
     limitation of liabilities and customer indemnification provisions (which
     limitation and indemnification will also benefit Supplier as the holder of
     the reagent or consumable portion of such AdNow leases); (viii) the right
     to enforce the customer's obligations regarding the location, maintenance
     and use of the Instruments(s); (ix) the benefit of any provisions on risk
     of loss, loss or damage to (including destruction of) the Instrument(s),
     including payments required from the customer if such events occur; (x) the
     right to possession of the Instrument(s) at the end of the term of such
     AdNow lease; (xi) the benefit of representations made by the customer
     (which representations will also benefit Supplier as the holder of

                                      -21-
<PAGE>

     the reagent or consumable portion of such AdNow leases); (xii) the benefit
     of the assignment provisions as they relate to the Instrument(s) and the
     Instrument Portion (as otherwise set forth in this paragraph) of such AdNow
     lease; (xiii) the benefit of the default and remedy provisions relating to
     the Instrument(s) and the Instrument Portion (as otherwise set forth in
     this paragraph) of such AdNow lease, including the right to declare and
     enforce a default against the customer; and (xiv) the benefit of
     miscellaneous provisions of the AdNow lease as they relate to the
     Instrument(s) and the Instrument Portion (as otherwise set forth in this
     paragraph) of such AdNow lease, such as the following provisions: entire
     agreement, governing law, amendment, waiver of jury trial, affect of
     invalidity of a provision, survival, disclosures under the Social Security
     Act and strict performance.

          (ii)  Effective upon the assignment and assumption of Distributor's
     rights and obligations relating to the reagent or consumable portion of the
     Valid Active AdNow Leases and the Valid Inactive AdNow Leases pursuant to
     subsection (i) above, Supplier and Distributor agree that all Valid Active
     AdNow Lease and Valid Inactive AdNow Lease customers shall pay all amounts
     due and owing under such AdNow leases with respect to the reagents or
     consumables (other than amounts invoiced by Distributor to customers prior
     to such assignment and assumption) to Supplier instead of Distributor.

          (iii) At the time of the assignment and assumption of Distributor's
     rights and obligations relating to the reagent or consumable portion of the
     Valid Active AdNow Leases and the Valid Inactive AdNow Leases pursuant to
     subsection (i) above, with respect to any Valid Active AdNow Lease or Valid
     Inactive AdNow Lease for which (A) Distributor has actually received a
     written notice of termination from the customer, (B) the customer is
     attempting to terminate because of any Supplier Responsibility Reason or
     Dual Responsibility Reason and (C) such breach or failure has not been
     cured nor have reasonable steps been taken to cure such breach or failure,
     Supplier shall pay to Distributor (x) in cases of attempted termination
     because of any Supplier Responsibility Reason, the Agreed Net Book Value of
     the Instrument(s) subject to that AdNow lease, and (y) in cases of
     attempted termination because of any Dual Responsibility Reason, 50% of the
     Agreed Net Book Value of the Instrument(s) subject to that AdNow lease;
     provided, however, that Supplier shall have no obligation to make the
     --------  -------
     payments specified in this subsection (iii) for any Instrument subject to a
     Valid Active AdNow Lease or Valid Inactive AdNow Lease which has been
     purchased by a third party leasing agent.

          (iv)  Unless a Third Party Transaction has been consummated,
     Distributor and Supplier shall enter into a mutually acceptable agency
     agreement ("Agency Agreement") whereby (A) Distributor shall appoint
     Supplier as its agent for purposes of (x) billing the customers for the
     Instrument Surcharge under the Valid Active AdNow Leases and, for a maximum
     period of nine months, under the

                                      -22-
<PAGE>

     Valid Inactive AdNow Leases and (y) collecting such Instrument Surcharge
     from the customers on behalf of Distributor; (B) Supplier agrees to assume
     all duties and obligations with respect to billing and collecting,
     including all record-keeping functions related thereto, being performed by
     Distributor as of the effective date of the Fourth Amendment to this
     Agreement with respect to the AdNow leasing program (it being understood
     that Distributor will have no further obligations under the AdNow leasing
     program); (C) all Valid Active AdNow Lease customers and Valid Inactive
     AdNow Lease customers shall pay all amounts due and owing with respect to
     the Instrument Surcharge under such Valid Active AdNow Leases and Valid
     Inactive AdNow Leases (other than amounts invoiced by Distributor to
     customers prior to the effective date of the Agency Agreement) to Supplier,
     as collection agent for Distributor, instead of to Distributor directly;
     (D) Distributor agrees to indemnify and hold Supplier harmless from claims
     by any Valid Inactive AdNow Lease customer, including reasonable attorney's
     fees, penalties and other out-of-pocket costs, if it is determined that the
     Instrument Surcharges collected by Supplier and paid to Distributor under
     the Agency Agreement for the nine-month period of time set forth herein,
     are not owed by such customer; and (E) Supplier agrees that, during the
     term of the Agency Agreement, it shall deliver its quarterly financial
     statements in the form of its Form 10-Q to Distributor within 45 days after
     the end of each calendar quarter and its audited financial statements
     within 90 days after the end of each calendar year. Supplier and
     Distributor agree that such Agency Agreement shall (A) be immediately
     terminable by Distributor upon an Event of Default and (B) terminate
     automatically each calendar month unless Distributor has sent a written
     notice to Supplier on or before the last day of such calendar month
     requesting an extension of such Agency Agreement for an additional month,
     in which case the Agency Agreement shall be automatically extended for one
     additional calendar month (in the event that no such extension request is
     sent by Distributor, then the Agency Agreement will terminate effective
     upon the earlier of (x) the date set forth in a written notice by
     Distributor to Supplier as being the date upon which Distributor will be
     capable of assuming the administration of the AdNow leasing program, and
     (y) the date which is 120 days after the last day of the month for which no
     request for extension is sent. Supplier shall provide services pursuant to
     the terms of the Agency Agreement at no charge to Distributor. At the
     effective time of the termination of the Agency Agreement, (x) with respect
     to those Valid Active AdNow Leases previously subject to the Agency
     Agreement which involve Instrument(s) that have a Net Book Value at that
     time, and (y) for the period of time ending on the date which is nine
     months after the effective time of commencement of the Agency Agreement,
     with respect to those Valid Inactive AdNow Leases previously subject to the
     Agency Agreement: (A) Distributor and Supplier agree that they will
     commence operating under the provisions of this Agreement which are set
     forth in Schedule 2 to the Fourth Amendment to this Agreement, as such
              ----------
     sections have been amended and supplemented to such date and as they are
     otherwise amended in such Schedule 2, with respect to both the reagent or
                               ----------
     consumables portion and the Instrument Portion of such AdNow leases, (B)
     Supplier shall take all actions necessary or

                                      -23-
<PAGE>

     appropriate, or that Distributor may reasonably request, to facilitate the
     prompt and efficient transfer of responsibilities of Supplier under the
     Agency Agreement and under the reagent and consumable portion of such AdNow
     leases to Distributor, including without limitation, transferring to
     Distributor all records (including computer data), correspondence and
     documents requested by Distributor related to such AdNow leases, and (C)
     all customers under such AdNow leases shall pay all amounts due and owing
     under such AdNow leases to Distributor instead of Supplier and Distributor
     shall have the authority to so notify customers. On the date which is nine
     months after the date of the Agency Agreement, provided that the Agency
     Agreement has not been terminated before such time, Distributor will assign
     to Supplier all of its right, title and interest in the Instruments subject
     to the Valid Inactive AdNow Leases.

          (v)  Unless a Third Party Transaction has been consummated, Supplier
     shall remit to Distributor on the fifteenth (15th) day of every month,
     beginning the second month after the date of the expiration or termination
     of this Agreement (and if the 15th falls on a weekend or holiday, then on
     the next business day following the 15th), (A) all collections received
     during the previous month from customers with respect to the Instrument
     Surcharge under all AdNow leases which are either Valid Active AdNow Leases
     or Valid Inactive AdNow Leases at the time of expiration or termination of
     this Agreement (the "Monthly Instrument Collections") (which remittance
     obligation shall be in Supplier's capacity as collection agent under the
     Agency Agreement), and (B) an amount equal to the positive difference, if
     any (any such difference a "Monthly Instrument Shortfall Payment") between
     (1) the Monthly Instrument Payment for the previous month under each AdNow
     lease which is a Valid Active AdNow Lease at the time of expiration or
     termination of this Agreement, minus (2) the aggregate amount of all
     collections received from customers with respect to the Instrument
     Surcharge under all Valid Active AdNow Leases during the previous month
     (which remittance obligation shall be a direct obligation of Supplier
     arising pursuant to this Agreement whether or not the Agency Agreement is
     then in effect; if the Agency Agreement is not then in effect and no funds
     are then available in the escrow account established pursuant to Section
                                                                      -------
     9(e)(vi), Distributor shall have the right to offset and deduct the amount
     --------
     of any Monthly Instrument Shortfall Payments due from Supplier from any
     amounts Distributor owes Supplier under Section 5(c) of this Agreement or
                                             ------------
     otherwise). Subject to Section 5(u), Supplier shall continue to pay to
                            ------------
     Distributor the Monthly Instrument Shortfall Payments for each Valid Active
     AdNow Lease until the Net Book Value of the Instrument(s) subject to the
     Valid Active AdNow Leases has been fully amortized or paid in full.
     Supplier shall begin to remit the Monthly Instrument Shortfall Payments to
     Distributor beginning on the 15th day of the second month after the date of
     the expiration or termination of this Agreement regardless of whether or
     not the lease identification process or the assignment or the assumption
     described herein have been effected. If the lease identification process
     has not been completed or the assignment or assumption have not been
     effected at such time, Distributor shall

                                      -24-
<PAGE>

     provide Supplier with the amount of each Monthly Instrument Shortfall
     Payment, then Supplier shall remit each such Monthly Instrument Shortfall
     Payments for each Active AdNow Lease (at the time of expiration or
     termination of this Agreement); provided that, for purposes of this
                                     --------
     sentence, Distributor may assume that the amount of each Monthly Instrument
     Shortfall Payment is equal to the monthly behind lease variance for such
     AdNow lease. Within 30 days after the identification process and the
     assignment and assumption is completed, Distributor will reimburse to
     Supplier any such Monthly Instrument Shortfall Payments made by Supplier on
     any Active AdNow Lease that is determined not to be a Valid Active AdNow
     Lease at the time of the expiration or termination of this Agreement, minus
     the aggregate amount by which the Monthly Instrument Shortfall Payments for
     the Valid Active AdNow Leases exceeds the amount assumed for the purposes
     of the preceding sentence.

          (vi) Unless a Third Party Transaction has been consummated, upon the
     earlier of (A) the assignment and assumption of the appropriate rights and
     obligations relating to the reagent or consumable portion of the Valid
     Active AdNow Leases and the Valid Inactive AdNow Leases pursuant to
     subsection (i) above, and (B) the date which is one day prior to Supplier's
     first payment date pursuant to subsection (v) above, Distributor shall pay
     the Distributor Loss Pool Amount to a third party escrow agent to be held
     in an escrow account in Distributor's name established pursuant to an
     escrow agreement in form and substance reasonably acceptable to Distributor
     and Supplier. Thereafter, the parties agree that amounts may be withdrawn
     from the escrow account only (i) by the Supplier directing the escrow agent
     to make payment of the specified amount to itself as reimbursement for its
     payment of any amount as part of a Monthly Instrument Shortfall Payment,
     (ii) by the Distributor directing the escrow agent to make payment to
     Distributor of any portion of the Monthly Instrument Collections or the
     Monthly Instrument Shortfall Payment which is not received by Distributor
     in a given month unless Distributor has received a notice from Supplier as
     to such amount pursuant to Section 13(n)(iii) or 16(d), (iii) by the
                                ------------------    -----
     Distributor directing the escrow agent to make payment to Distributor of
     the amount then remaining in the escrow account if the Supplier is then the
     subject of any bankruptcy, Insolvency or similar proceeding so long as
     Distributor has resumed the distribution relationship described in
     subsection (iv) above, and (iv) any remaining amount (if any, after giving
     effect to withdrawals made pursuant to clauses (i), (ii) and (iii) of this
     paragraph) by the Supplier, if all of the Instruments have been fully
     amortized, paid in full or purchased by a third party leasing agent. The
     escrow agent's fees under the escrow agreement described herein shall be
     shared equally by Distributor and Supplier.

          The parties further agree that such Distributor Loss Pool Amount shall
     be Supplier's sole and exclusive recourse to Distributor (even if the
     amount available thereunder is zero) for all potential recourse against
     Distributor in connection with the Leased Instrument portfolio (subject to
     the next sentence). It is understood

                                      -25-
<PAGE>

     that after the Distributor Loss Pool Amount is paid to the third party
     escrow agent Supplier shall have no additional recourse against Distributor
     for any claims, liabilities, damages, losses or expenses relating to the
     Valid Active AdNow Leases or the Valid Inactive AdNow Leases (including
     claims relating to any amounts unpaid by customers under, or claims
     relating to, any Valid Active AdNow Lease or Valid Inactive AdNow Lease
     (including the Monthly Instrument Shortfall Payments)), other than (A)
     amounts owed by Distributor for personal property taxes assessed on any
     Instrument subject to a Valid Active AdNow Lease or a Valid Inactive AdNow
     Lease for the period prior to the assignment, if any, of such Instrument to
     Supplier, and (B) losses which are incurred by Supplier as a direct result
     of either Distributor's failure to file any UCC financing statement or
     Distributor's failure to insure any of the Instruments.

                 Supplier will provide to Distributor any information in its
     possession regarding the Instrument(s) subject to each Valid Active AdNow
     Lease and each Valid Inactive AdNow leases in order for Distributor to bill
     and collect the personal property taxes assessed on any Instrument subject
     to any such AdNow lease.

          (vii)  If at any time Supplier, a customer or a third party pays to
     Distributor the remaining Net Book Value of the Instruments subject to a
     Valid Active AdNow Lease or a Valid Inactive AdNow Lease, Supplier shall no
     longer be required to pay to Distributor any Monthly Instrument Shortfall
     Payments or Monthly Instrument Collections for such AdNow lease.

          (viii) For as long as Supplier has any obligation to remit any
     collections to Distributor under the Agency Agreement or to pay any Monthly
     Instrument Shortfall Payment to Distributor pursuant hereto, Supplier will
     provide to Distributor a report each month at the time it remits such
     payments to Distributor. Each report will break down the aggregate monthly
     payment made by Supplier to Distributor to indicate the portion thereof
     that is attributable to each AdNow lease and will identify the AdNow
     leases, if any, for which Supplier intends to cease making Monthly
     Instrument Shortfall Payments pursuant to Section 6(aa) hereof.
                                               -------------

     6.5  Lease Variances.  Section 13 of the Distribution Agreement is hereby
          ----------------
amended to add the following as a new subsection (m) thereof:

     Notwithstanding anything to the contrary in Section 4(b) of this Agreement,
                                                 ------------
     and except as provided in the Second Amendment to this Agreement including
     Exhibit C thereof, the February Letter Agreement or the Fourth Amendment to
     this Agreement, until expiration or termination of this Agreement,
     Distributor and Supplier acknowledge and agree that Distributor is fully
     responsible for and is

                                      -26-
<PAGE>

     fully entitled to the benefit of any lease variances (including any
     customer underpayments and overpayments) and the Net Book Value of all
     Instruments and the receivables relating to any AdNow lease (whether active
     or otherwise).

     6.6  Supplier Interference; Conversions. Section 6 of the Distribution
          ----------------------------------
Agreement is hereby amended to add the following as a new subsection (aa)
thereof::

     Until the termination or expiration of this Agreement, Supplier agrees it
     will not interfere with Distributor's right to collect any amounts related
     to AdNow leases from customers. Supplier shall, within 30 days after the
     date of the Fourth Amendment to this Agreement, send a notice to each
     member of its sales force (with a copy to Distributor), in form and
     substance reasonably acceptable to Distributor and will instruct each new
     member of its sales force at the time such person becomes a member, in each
     case to the effect that they do not have the authority to release any
     customer from any obligations to Distributor under its AdNow lease and,
     therefore, they should not make any statements to such customers or
     otherwise imply to such customers anything to the contrary. Notwithstanding
     any other provision of this Agreement, or the Fourth Amendment hereto, or
     the Settlement Agreement, with respect to any Instrument that Supplier
     removes from a customer's facility or receives from a customer with
     Supplier's written approval, in each case without Distributor's consent, or
     that Supplier replaces or supersedes with any other equipment (including
     any other Instrument) (any such action shall be referred to herein as a
     "Conversion"):

          (i)   for any Conversion made during the Term of this Agreement, if
     such Instrument is then subject to an Active AdNow Lease, Supplier shall
     pay to Distributor the Net Book Value of the Instrument (or other Products
     associated with such Instrument) and all net behind lease variances, in
     each case calculated at the time of the Conversion (irrespective of whether
     any portion of such net behind lease variances arose prior to the date of
     the Fourth Amendment hereto);

          (ii)  for any Conversion of a Stratus Instrument made on or after
     April 15, 2000 but during the Term of this Agreement (irrespective of
     whether such Conversion was made prior to the date of the Fourth Amendment
     hereto), if such Instrument is (or was) then subject to any of the AdNow
     leases listed on Schedule 3, Supplier shall pay to Distributor all net
                      ----------
     behind lease variances calculated as of April 15, 2000 (irrespective of
     whether any portion of such net behind lease variances arose prior to the
     date of the Fourth Amendment hereto);

          (iii) for any Conversion of a Paramax Instrument, Supplier shall have
     no payment obligations to Distributor;

                                      -27-
<PAGE>

          (iv) for any Conversion made during the Term of this Agreement, if
     such Instrument is then subject to an AdNow lease that is within its
     renewal term, Supplier shall notify such customer in writing (with a copy
     to Distributor) that the new equipment arrangement does not release such
     customer from any obligations to Distributor under its AdNow lease; and

          (v)  for any Conversion made after the expiration or termination of
     this Agreement, if such Instrument is then subject to an AdNow lease for
     which Supplier is remitting Monthly Instrument Shortfall Payments to
     Distributor, Supplier shall accelerate its payments of Net Book Value of
     the Instrument (or other Products associated with such Instrument) and pay
     to Distributor the Net Book Value of the Instrument, calculated at the time
     of the Conversion.

     Supplier further agrees that it shall use commercially reasonable efforts
     to notify Distributor on a monthly basis of any Conversion or intent to
     Convert any Instrument subject to an AdNow lease. Distributor and Supplier
     acknowledge and agree that the provisions of this Section 6(aa) supersede
                                                       -------------
     Section A(3) of the February Letter Agreement and Section II.F.3 of Exhibit
     C to the Second Amendment to this Agreement.

     6.7  Distributor Interference; Conversions. Section 5 of the Distribution
          -------------------------------------
Agreement is hereby amended to add the following as a new subsection (u)
thereof:

     Upon and after the earliest to occur of (i) the consummation of a Third
     Party Transaction pursuant to Section 13(k) of this Agreement, (ii) the
                                   -------------
     termination or expiration of this Agreement, and (iii) as to AdNow leases
     involving MicroScan Products only, the time that Distributor first
     manufactures, sells, leases, solicits orders for or otherwise distributes
     in the Territory any products that are competitive with the MicroScan class
     of Products, Distributor will not interfere with (x) Supplier's right to
     collect any amounts relating to the reagent or consumable portion of any
     Valid Active AdNow Lease or Valid Inactive AdNow Lease from customers or
     (y) while the Agency Agreement is in effect, the Monthly Instrument
     Collections. Distributor further agrees that it will not, after the
     applicable date set forth in the preceding sentence, release any customer
     from, or modify any obligation of a customer under, its Valid Active AdNow
     Lease which release or modification would create or increase any liability
     of Supplier (either by creating additional recourse due from Supplier to
     the third party leasing agent in the event a Third Party Transaction is
     consummated or by increasing the amount of the Monthly Instrument Shortfall
     Payments due). Upon and after the expiration or termination of this
     Agreement, at the time, if any, that Distributor replaces an Instrument
     subject to such an AdNow lease with another piece of equipment:

                                      -28-
<PAGE>

          (i)  if such Instrument is then subject to a Valid Inactive AdNow
     Lease, Distributor shall notify such customer in writing (with a copy to
     Supplier) that the new equipment arrangement does not release such customer
     from any obligations to Supplier for the reagent or consumable portion of
     its AdNow lease; and

          (ii) if such Instrument is then subject to an AdNow lease for which
     Supplier is remitting Monthly Instrument Shortfall Payments to Distributor,
     Supplier shall no longer be required to remit any Monthly Instrument
     Shortfall Payment for such AdNow lease; provided that Supplier (x) gives
                                             --------
     Distributor advance notice of its intention to cease making any Monthly
     Instrument Shortfall Payments, along with commercially reasonable
     documentation that demonstrates Supplier's entitlement to cease such
     payments pursuant to this Section, and (ii) follows the procedure outlined
     in Section 16(d).
        -------------

                              VII. PAYMENT TERMS

     7.1  Guaranteed Gross Profit Margin. Effective January 1, 2001, Section I
          ------------------------------
of Exhibit A to the Distribution Agreement is hereby amended to change the
guaranteed gross profit margins for the following classes of Products for the
Remaining Term of Agreement to the percentages indicated:


                                             Remaining Term
          Class of Product                    of Agreement
          ----------------                   --------------

          Dade Hemostasis, excludes CVDI          6.5%
          MicroScan                               6.5%
          Other Dade                              6.5%


     7.2  Offsets or Deductions; Expedited Dispute Resolution Process Matters.
          -------------------------------------------------------------------
Section 13 of the Distribution Agreement is hereby amended to add the following
as a new subsection (n) thereof:

          (i)  Unless specifically agreed to in writing by Supplier, or awarded
     to Distributor under the dispute resolution processes set forth in Section
                                                                        -------
     16 of this Agreement, and except as set forth in Section II.F.1 of Exhibit
     --
     C to the Second Amendment to this Agreement (although the parties
     acknowledge that the

                                      -29-
<PAGE>

     provisions of Section 13(n)(ii)(E) supersede the foregoing provisions of
                   --------------------
     Exhibit C with respect to the process to be followed for settling amounts
     related to Conversions), Distributor shall not deduct or offset any amounts
     it believes are due and owing it by Supplier from any amounts Distributor
     owes Supplier under Section 5(c) of this Agreement or otherwise; provided,
                         ------------                                 --------
     however, that solely in the following circumstances Distributor may deduct
     -------
     or offset amounts owing by Supplier against amounts owing to Supplier:

          (A)  Adjustments relating to disputes on Product receipts and rebates
       under the automated or manual Vendor Rebate System (such rebates do not
       include amounts for retroactive Instrument Surcharges described in
       subsection (I) below) relating to Products sold to customers in the
       current month and the advance rebate set forth in Section 4(c) of this
                                                         ------------
       Agreement;

          (B)  Surcharge amounts relating to Hemostasis Instruments subject to
       the Columbia/HCA contracts or successor accounts;

          (C)  Inbound freight charges where Distributor has incurred freight
       charges to transport Product from Supplier's facilities to Distributor's
       distribution centers;

          (D)  Administrative fees and rebates described in Sections 5(a) and
                                                            -------------
       5(e)(14) of this Agreement;
       --------

          (E)  The amounts payable to Distributor under the April Letter
       Agreement;

          (F)  Preauthorized factory returns;

          (G)  The traced sales fee set forth in Section 5(o) of this Agreement;
                                                 ------------

          (H)  Twenty-five percent (25%) of the value of a Value Bond where a
       customer has used the Value Bond toward the lease or purchase of
       Products;

          (I)  The Instrument Surcharge amounts set forth in Section 13(q) of
                                                             -------------
       this Agreement; and

          (J)  If the Agency Agreement is not in effect and no funds are then
       available in the escrow account established pursuant to Section 9(e)(vi),
                                                               ----------------
       the amount of any Monthly Instrument Shortfall Payment due from Supplier.

                                      -30-
<PAGE>

          Prior to or simultaneously with taking any of the foregoing
     deductions or offsets, Distributor shall provide Supplier with
     documentation, similar to documentation that has been
     historically presented, demonstrating Distributor's entitlement
     to the offset or deduction.

          (ii) Distributor and Supplier agree that each of the
     following claimed deductions (or entitlements to cease making
     certain payments, as the case may be) shall be subject to the
     Expedited Dispute Resolution Process set forth in Section 16(d)
                                                       -------------
     of this Agreement:

          (A)   Any rebates under the automated or manual Vendor
       Rebate System other than those covered in Section 13(n)(i)(A);
                                                 -------------------

          (B)   The Net Purchase Price of Saleable Inventory unpaid by
       Supplier pursuant to the terms of Section 6(a)(2) of this
                                         ---------------
       Agreement;

          (C)   Amounts payable to Distributor pursuant to the terms
       of Sections 5(v), 6(h), 6(w), or 6(x) of this Agreement;
          -------------  ----  ----

          (D)   Any duplicate payments of Monthly Instrument Shortfall
       Payments due to Supplier; provided that Supplier shall not be
                                 --------
       entitled to any recovery of any overpayments made to
       Distributor unless claims for such are presented to Distributor
       for payment within twelve (12) months after the date of such
       overpayment;

          (E)   Amounts payable to Distributor pursuant to the terms
       of Section 6(aa) of this Agreement and Supplier's entitlement
          -------------
       to cease making any Monthly Instrument Shortfall Payments
       pursuant to the terms of Section 5(u) of this Agreement;
                                ------------

          (F)   Any claim by Supplier that Distributor improperly
       deducted or offset any amount under Section 13(n)(i) of this
                                           ----------------
       Agreement; and

          (G)   Any claim by Distributor that Supplier improperly
       deducted or offset any amount under Section 13(n)(iii) of this
                                           ------------------
       Agreement.

          (iii) Unless specifically agreed to in writing by
     Distributor or awarded to Supplier under the dispute resolution
     processes set forth in Section 16 of this Agreement, Supplier
                            ----------
     shall not take any deductions from or otherwise reduce or cease
     paying to Distributor any amount collected from customers as
     agent for Distributor under the Agency Agreement, any Monthly
     Instrument Shortfall Payment or any other amount owed
     Distributor; provided, however, that Supplier may deduct or
                  --------  -------
     offset any duplicate payment of any Monthly Instrument Shortfall

                                      -31-
<PAGE>

     Payment owing by Distributor from Supplier's payment of future
     Monthly Instrument Shortfall Payments only if the following
     conditions are met: (x) Supplier presents its claim to
     Distributor for recovery of any such overpayment within twelve
     (12) months after the date of such overpayment and (y) Supplier
     provides Distributor, at least 15 days prior to taking any such
     deduction, with commercially reasonable documentation that
     demonstrates Supplier's entitlement to the offset or deduction.

          (iv)  Distributor and Supplier agree that any deduction or
     offsetting of monies, including any cessation of payments (other
     than the deductions and offsets specified in this Section 13(n)),
                                                       --------------
     by Distributor or Supplier, as the case may be, from monies owed
     to the other party will result in irreparable harm to such party,
     that such party would not have an adequate remedy at law for such
     deduction or offset, and that in the event of a deduction or
     offset, in addition to other remedies available to it by law,
     such party shall be entitled to obtain injunctive relief in a
     court or arbitration.

          (v)   If at any time Supplier owes amounts to Distributor
     which are subject to deduction or offset pursuant to the terms of
     this Section 13(n) (including as provided in Section II.F.1 of
          -------------
     Exhibit C to the Second Amendment to this Agreement, subject to
     the acknowledgement set forth in Section 13(n)(i)), but
                                      -----------------
     Distributor owes no (or owes inadequate) amounts to Supplier from
     which to deduct such Supplier-owed amounts, Supplier shall be
     invoiced for such Supplier-owed amounts and shall pay such
     undisputed amounts on net 30 day terms (any disputed amounts
     shall be paid pursuant to the terms of the resolution of the
     dispute).

     7.3  Rebates on Unsold Products. Section 4(b) of the Distribution Agreement
          --------------------------
is hereby amended to add the following as a new subsection (8) thereof:

     Beginning on the effective date of the Fourth Amendment to this
     Agreement, in the event that Distributor has not been able to
     sell a Product to a customer because (i) it is expired, (ii) has
     been damaged or destroyed (but has not been returned to
     Supplier), (iii) is lost and has not been found (but excluding
     adjustments to Distributor's records associated with the Return
     Process) or (iv) has been donated to a charitable organization,
     Distributor shall be entitled to a rebate from Supplier equal to
     the difference between the invoice price (as described in this
     Section 4) of the Product from Supplier to Distributor and the
     ---------
     average selling price to the customer, minus Distributor's
     guaranteed gross profit margin. Distributor shall only be
     entitled to this rebate if the request for such rebate is made
     within nine (9) months after the expiration, damage, destruction,
     loss or donation of the Product and then only if Distributor
     provides Supplier with the following documentation:

                                      -32-
<PAGE>

          (a)   If the rebate amount is less than $250,000 in any one
     calendar year, Distributor must provide Supplier with summary
     level bounce detail, including physical inventory or cycle count
     adjustments, catalog numbers, amount of inventory and reasons for
     the "bounce", supporting the amount of the rebate.

          (b)   If the rebate amount exceeds $250,000 in any one
     calendar year, Distributor must provide for every Product which
     exceeds the $250,000 amount, commercially reasonable
     documentation showing the relevant information related to the
     Product.

          (i)   For donated Product, such documentation will consist
                of a copy of the letter either from Distributor or the
                charitable organization acknowledging the donation;

          (ii)  For warehouse shortages, physical inventories, cycle
                counts and adjustments, such documentation will
                consist of information showing that overages and
                shortages were netted against each other; and

          (iii) For damaged, destroyed or expired Product, such
                documentation will consist of a certificate of
                destruction.

     7.4  Supplier Receivables.  Nothing in the Distribution Agreement, the
          --------------------
Settlement Agreement or this Fourth Amendment shall bar Supplier from claiming
that amounts are due from Distributor for Distributor's purchase of Products
from Supplier, including aged receivables and receivables allegedly incurred
prior to this Fourth Amendment, although Distributor does not agree or concede
that it owes any particular amount.

     7.5  Payments Received.  Section 13 of the Distribution Agreement is hereby
          -----------------
amended to add the following as a new subsection (o) thereof:

     Each of Supplier and Distributor agrees that if it receives any
     payment from any customer that is owed to the other party, it
     will remit such amount to the other party within thirty (30) days
     of receipt thereof.

                                      -33-
<PAGE>

                               VIII. TRANSITION

     8.1  Transition Payment.  Distributor hereby acknowledges receipt from
          ------------------
Supplier of an irrevocable Two Million Dollar ($2,000,000) transition fee. This
transition fee is for services rendered by Distributor to Supplier and Supplier
acknowledges and agrees that it shall not under any circumstances have recourse
back to Distributor for any portion of the transition fee, including but not
limited to a claim by Supplier that Distributor has breached the terms of this
Fourth Amendment.

     8.2  Assignment of Contracts.  The third sentence of Section 9(a) of the
          -----------------------
Distribution Agreement is hereby amended in its entirety to read as follows:

     With respect to the customer contracts referred to in the
     previous sentence, within a commercially reasonable time prior to
     the expiration or termination of this Agreement, Distributor
     agrees to use its commercially reasonable efforts to identify,
     and begin the process to assign and otherwise transition to
     Supplier (to the extent permitted thereunder) all such contracts
     which consist of all customer purchase orders, contracts and
     commitments (excluding AdNow leases and the Federal Supply
     Schedule Contracts), including all health systems and multisystem
     contracts and commitments relating to the Products and upon the
     termination or expiration, agrees to assign such contracts, to
     the extent permitted thereunder; provided, however, that in the
                                      --------  -------
     event any such contract relates to products other than Supplier's
     Products, then Distributor's obligations hereunder relate only to
     the portion of the contract related to Supplier's Products.

     8.3  Government Contracts.  Section 13 of the Distribution Agreement is
          --------------------
hereby amended to add the following as a new subsection (s) thereof:

     With respect to government leases:

          (i)  Distributor agrees to provide Supplier with
     commercially reasonable assistance in training its government
     sales department including, but not limited to, allowing
     Supplier's employees to observe, meet with and discuss with
     Distributor's employees Distributor's government program.

                                      -34-
<PAGE>

          (ii) Supplier agrees that, as soon as practically possible,
     it will submit to the government a request to include its
     Products on its own Federal Supply Schedules. Distributor agrees
     that it will provide reasonable assistance to Supplier in
     connection with Supplier's submission. Upon the acceptance of
     Supplier's submission by the appropriate governmental agency,
     Distributor will cancel its own Federal Supply Schedules relating
     to Supplier's Products and use reasonable efforts to assign to
     Supplier Distributor's cost per test and cost per reportable
     Federal Supply Schedule leases.

     8.4  Transition Information.  Section 5 of the Distribution
          ----------------------
Agreement is hereby amended to add the following as a new subsection
(v) thereof:

     Distributor agrees to provide Supplier, within a commercially
     reasonable time, such information in its possession pertinent to
     Supplier's business, to the extent it is readily available in
     automated form, as Supplier reasonably requests, in order for
     Supplier to smoothly transition the distribution business from
     Distributor to Supplier. Supplier shall pay to Distributor the
     reasonable direct costs of the preparation and transfer of such
     information. In addition, Distributor shall provide Supplier or
     the third party leasing agent, as the case may be, with a copy of
     all Valid Active AdNow Lease files at no charge to Supplier or
     such third party leasing agent.

     8.5  Transition Principles. Section 13 of the Distribution
          ---------------------
Agreement is hereby amended to add the following as a new subsection
(p) thereof:

     The parties agree that they will work together in good faith to
     effect an orderly and expeditious transition of the distribution
     of Products from Distributor to Supplier. The parties
     specifically agree that they will coordinate their customer
     communications.

                            IX. SURCHARGE REMOVALS

     9.1  Surcharge Removals. Section 13 of the Distribution Agreement
          ------------------
is hereby amended to add the following as a new subjection (q)
thereof:

     Notwithstanding anything contained in the Fourth Amendment to
     this Agreement or the Settlement Agreement to the contrary,
     Distributor shall be entitled to receive from Supplier those
     Instrument Surcharges that were not properly

                                      -35-
<PAGE>

     calculated or removed by Distributor up to an amount not to be
     exceed Five Hundred Thousand and 00/100 Dollars ($500,000) even
     if such surcharge was incurred prior to the date of the Fourth
     Amendment to this Agreement; provided, however, that such limit
                                  --------  -------
     does not apply where such failure to properly calculate or remove
     those Instrument Surcharges is a result of a computer systems
     failure of Distributor's computerized surcharge removal system
     and any Instrument Surcharges not properly calculated or removed
     for this reason shall not be calculated as part of the foregoing
     limit. Notwithstanding the above, Supplier must provide
     Distributor with written notice of Product substitutions at least
     fifteen (15) days in advance of such substitution or Distributor
     shall be entitled to reimbursement by Supplier of Instrument
     Surcharge amounts not withheld by Distributor as a result of
     Supplier's failure to notify Distributor and such amounts due
     shall not be subject to or calculated as part of the foregoing
     limit. From the date of the Fourth Amendment to this Agreement
     forward, Distributor shall only be entitled to retroactive
     Instrument Surcharge if claims for such are presented to Supplier
     for payment within twelve (12) months after the date the Product
     associated with the Instrument Surcharges was invoiced to the
     customer. It being understood and agreed that if Distributor
     sells the Instrument(s) subject to an AdNow lease to a third
     party leasing agent, if Supplier pays Distributor the Net Book
     Value of the Instrument(s) subject to any AdNow lease pursuant to
     the February Letter Agreement, or if Distributor and the customer
     agree to an early buy-out of the Instrument(s) subject to an
     AdNow lease and the customer has paid Distributor the agreed-upon
     amount for such early buy-out, Distributor shall not be entitled
     to remove any further Instrument Surcharges under such AdNow
     lease.

                                X. VALUE BONDS

     10.1  Retirement of Value Bonds.  Distributor, Supplier and Dade Behring
           --------------------------
Holdings, Inc., formerly known as Diagnostics Holding, Inc., agree that
Distributor shall no longer be required to honor any outstanding Value Bonds.

                      XI. EXPEDITED ARBITRATION PROCEDURE

     11.1  Arbitration. (a) Section 16(b) of the Distribution Agreement is
           -----------
amended by adding the following clause to the beginning thereof:

     Except as to those types of deduction issues described in Section
                                                               -------
     13(n)(ii), as to which the Expedited Dispute Resolution Process
     ---------
     described in Section 16(d) applies," [Section 16(b) then
                  -------------
     continues: "any dispute that cannot...."]

                                      -36-
<PAGE>

     (b)  Section 16 of the Distribution Agreement is hereby amended
to add the following as a new subsection (d) thereof:

     The parties agree that the deductions described in Section
                                                        -------
     13(n)(ii) of this Agreement shall be resolved as follows:
     --------

          (i)   The party making a claim shall provide a written
     summary of the claim entitled "OFFICIAL CLAIM UNDER SECTION
     16(d)" to the non-claiming party along with commercially
     reasonable documentation that demonstrates the claiming party's
     entitlement to such claim; provided that neither party may make a
                                --------
     claim under this Section based upon Section 13(n)(ii)(E) unless
                                         --------------------
     (A) the claiming party previously sent an informal notice of the
     claim to the non-claiming party and either (x) a commercially
     reasonable period of time has passed since the date of such
     informal notice and during such time the parties have engaged in
     negotiations, including senior management review by the claiming
     party, in an attempt to resolve such claim and such claim remains
     unresolved, or (y) the non-claiming party failed to respond to
     such informal notice within 14 days after the date of such
     notice, and (B) the claiming party includes in its official claim
     pursuant to this Section a certificate signed by a member of its
     senior management to such effect.

          (ii)  The non-claiming party shall have fourteen (14) days
     to accept or reject all or any portion of the other party's
     claim.

          (iii) If the non-claiming party fails to respond within
     such fourteen (14) day period, the entire claim shall be deemed
     accepted by the non-claiming party.

          (iv)  If the non-claiming party accepts any portion of the
     claim, then the claiming party shall be entitled under Section
                                                            -------
     13(n) to deduct such undisputed portion from amounts owed to it
     -----
     by the non-claiming party or, in the event that insufficient
     funds are available for deduction, then the non-claiming party
     shall pay to the claiming party, pursuant to Section 13(n)(v),
                                                  ----------------
     that portion of the undisputed claim that is not deducted.

          (v)   If the non-claiming party rejects any portion of the
     claim then the parties agree that they will attempt to settle,
     within fourteen (14) days of the rejection of the claim by the
     non-claiming party, such rejected portion of the claim through
     good faith negotiations in the spirit of mutual cooperation
     between senior business executives with authority to resolve such
     claim.

          (vi)  If within such fourteen (14) day period the parties'
     senior executives fail to settle such disputed portion of the
     claim, the parties agree to submit such claim in writing together
     with all supporting documentation therefor

                                      -37-
<PAGE>

     to binding arbitration before the Agreed Arbitrator. The parties
     agree to designate such person within three (3) weeks of the
     first arbitration notice under this Section 16(d).
                                         -------------

          (vii)  Upon submission of the claim to the Agreed
     Arbitrator, the parties agree that the non-claiming party shall
     have fourteen (14) days to respond to the claiming party's
     submission.

          (viii) The Agreed Arbitrator shall have fourteen (14) days
     from the submission of the non-claiming party's response to issue
     a written decision.

          (ix)   The parties agree that such Agreed Arbitrator shall
     apply the substantive laws of the State of Illinois including but
     not limited to the law concerning applicable burdens of proof in
     reaching his or her decision and shall use the Federal Rules of
     Evidence in determining the sufficiency of the evidence
     presented. Unless the parties agree otherwise, (x) neither party
     shall be entitled to discovery from the other and (y) neither
     party shall be entitled to discovery from third parties, unless
     such third party discovery is completed within fourteen (14) days
     after the claiming party's submission.

     The parties each agree to designate in writing one person at
     their respective companies to accept or reject such claims.
     Distributor's initial designated person shall be Teresa Hadad and
     Supplier's initial designated person shall be Nancy Krejsa. The
     parties agree that all claims and other communications pursuant
     to this Section 16(d) shall be in writing and shall be deemed to
             -------------
     have been given if delivered by hand, or sent by courier or
     facsimile transmission to the appropriate designated person;
     provided that in the case of facsimile transmission, a
     --------
     confirmation copy of the notice shall be delivered by hand or
     sent by courier within two (2) days of transmission. All notices
     given in accordance with this section shall be effective, if
     delivered by hand or by courier, at the time of delivery and, if
     communicated by facsimile transmission, at the time of
     transmission.

                              XII. MISCELLANEOUS

     12.1  Drafting.  This Fourth Amendment was negotiated at arms-length,
           --------
mutually-drafted and entered into freely by the parties with the advice and
assistance of counsel. In the event an ambiguity exists in any provision of this
Fourth Amendment, it shall not be construed against one of the parties to this
Fourth Amendment.

                                      -38-
<PAGE>

     12.2  Scope of Promises, Representations, and Inducements.  The parties
           ---------------------------------------------------
acknowledge, warrant and represent that no promises, representations or
inducements, except as set forth herein, and in the attached schedules or the
Settlement Agreement, have been offered or made by a party hereto to any other
party hereto to secure the execution of this Fourth Amendment, and that this
Fourth Amendment is executed without reliance on any statements or any
representations not contained herein or the Settlement Agreement.

     12.3  Voluntary Agreement.  Each of the parties certifies that it is
           -------------------
voluntarily entering into this Fourth Amendment in good faith based solely and
completely upon its own judgment and upon the advice and counsel of its own
attorneys following its good-faith assessment of the Arbitration, its claims and
defenses, and the provisions set forth in this Fourth Amendment and the attached
schedules.

     12.4  Survival.  Section 13 of the Distribution Agreement is hereby amended
           --------
to add the following as a new subsection (r) thereof:

     The parties hereby agree that notwithstanding anything to the
     contrary in this Agreement, (i) the following provisions shall
     survive the expiration or termination of this Agreement: (A)
     Sections 5(m), 5(q), 5(u), 6(m), 6(t), 6(aa), 9, 14 and 16 of
     -------------  ----  ----  ----  ----  -----  -  --     --
     this Agreement, (B) Section A(2) of the February Letter
     Agreement, and (C) any liabilities, obligations or duties then
     accrued or outstanding, and (ii) Sections 5(q) and 6(t) shall
                                      -------------     ----
     survive until the one-year anniversary of the date of the
     expiration or termination of this Agreement.

     12.5  Governing Law.  This Fourth Amendment shall be governed by and
           -------------
construed and interpreted in accordance with the laws of the State of Illinois,
applicable to contracts made and to be performed in that state and the federal
laws of the United States of America. Any lawsuit arising from or related to
this Fourth Amendment shall be brought before the United

                                      -39-
<PAGE>

States District Court for the Northern District of Illinois or an Illinois state
court sitting in Lake County, Illinois, or Cook County, Illinois. The parties
hereby consent to the jurisdiction of such courts. Nothing in this Section 12.5
is intended to alter the arbitration provisions of Section 16 of the
Distribution Agreement.

     12.6  Severability.  Section 13(f) of the Distribution Agreement is hereby
           ------------
amended to add the following sentence to the end thereof:

     To the extent permitted by applicable law, the parties hereto
     hereby knowingly and voluntarily waive any provision of law that
     prohibits or renders void or unenforceable any part, provision,
     representation or warranty hereof.

     12.7  Entire Agreement.  This Fourth Amendment embodies the entire
           ----------------
understanding between the parties regarding their amendments to the Distribution
Agreement, and the correspondence and other communications made in the course of
negotiating this Fourth Amendment are merged herein and replaced hereby.

     12.8  Successors and Assigns.  This Fourth Amendment shall be binding upon
           ----------------------
and inure to the benefit of the parties hereto and their successors and
permitted assigns; provided that this Fourth Amendment may only be assigned
concurrently with the Distribution Agreement, pursuant to Section 14 of the
Distribution Agreement. Nothing in this Forth Amendment, express or implied, is
intended or shall be construed to confer upon any entity or person other than
the parties and successors and assigns permitted by Section 14 of the
Distribution Agreement any right, remedy or claim under or by reason of this
Fourth Amendment.

     12.9  Modifications.  No part or provision of this Fourth Amendment may be
           -------------
changed, modified, waived, discharged or terminated except by a mutually
executed, signed written

                                      -40-
<PAGE>

agreement. The failure of a party to seek redress for violation of, or to insist
upon strict performance of, any provision of this Fourth Amendment shall not be
a waiver of that provision by that party or estop that party from asserting
fully any and all of its rights under this Fourth Amendment.

     12.10  Authorization to Sign. Each party hereby represents and warrants
            ---------------------
that the individual signing this Fourth Amendment on its behalf is duly
authorized to enter into this Fourth Amendment and to execute and legally bind
such party to it.

     12.11  Counterparts. This Fourth Amendment may be executed in counterparts,
            ------------
each of which shall constitute an original and all of which when taken together
shall constitute one and the same instrument.

     12.12  Headings.  The Headings used in this Fourth Amendment have been
            --------
inserted for convenience of reference only and do not define or limit the
provisions hereof.

     12.13  Confirmation. Except as expressly provided herein, the provisions of
            ------------
the Distribution Agreement remain in effect.

                                      -41-
<PAGE>

     IN WITNESS, WHEREOF, this Fourth Amendment has been executed by the
authorized representatives of the parties as of the date first written above.


Distributor:                  ALLEGIANCE HEALTHCARE CORPORATION

                                   /s/ [ILLEGIBLE]
                              ----------------------------------------
                              By:  [ILLEGIBLE]
                                 -------------------------------------
                              Its: VP /GM  SP Laboratory Business
                                  ------------------------------------


Supplier:                     DADE BEHRING INC.

                              ________________________________________
                              By: ____________________________________
                              Its: ___________________________________


FOR PURPOSES OF SECTIONS 10.1 AND 12.10 OF THIS FOURTH AMENDMENT ONLY:

                              DADE BEHRING HOLDINGS INC.
                              (f/n/a DIAGNOSTICS HOLDING, INC.)


                              ________________________________________
                              By: ____________________________________
                              Its: ___________________________________

                                      -42-
<PAGE>

     IN WITNESS, WHEREOF, this Fourth Amendment has been executed by the
authorized representatives of the parties as of the date first written above.


Distributor:                  ALLEGIANCE HEALTHCARE CORPORATION



                              ________________________________________
                              By: ____________________________________
                              Its: ___________________________________



Supplier:                     DADE BEHRING INC.



                                   /s/ [ILLEGIBLE]
                              ----------------------------------------
                              By:      [ILLEGIBLE]
                                 -------------------------------------
                              Its: Corporate Vice President
                                  ------------------------------------

FOR PURPOSES OF SECTIONS 10.1 AND 12.10 OF THIS FOURTH AMENDMENT ONLY:

                              DADE BEHRING HOLDINGS INC.
                              (f/n/a DIAGNOSTICS HOLDING, INC.)

                              /s/
                              ----------------------------------------
                              By:  [ILLEGIBLE]
                                 -------------------------------------
                              Its: President & COO
                                  ------------------------------------

                                      -43-
<PAGE>

                                                                      Schedule 1
                                                                      ----------

                 Terms of Distribution Agreement (as amended)
              which will Apply to the Unassigned AdNow Leases and
        to the Products Distributed under such Unassigned AdNow Leases
              (any items not listed herein will not be operative)

1.   Section 1 (Definitions)
2.   Section 2(a)(3), although the lead-in language of 2(a) will be amended to
     read in its entirety as follows:  "Supplier hereby grants to Distributor
     the non-exclusive right to sell the Hemostasis and MicroScan classes of
     Products throughout the Territory, subject to the following conditions and
     limitations"
3.   Section 2(b) will be amended to read in its entirety as follows:
     "Distributor hereby accepts such grant."
4.   Section 4
5.   Section 5(a) will be amended to read in its entirety as follows: "Supply
     Products to existing customers pursuant to all AdNow leases in existence at
     the expiration or termination of this Agreement, the reagents or
     consumables portion of which has not been assigned to Supplier pursuant to
     the terms of Section 9(e) of this Agreement."
6.   Section 5(b) and (c)
7.   Section 5(e)(1), (2), (3), (4); however, both the lead-in language and the
     unnumbered last paragraph of 5(e) are deleted
8.   Section 5(f)
9.   The first two sentences of Section 5(j)
10.  Section 5(m), (n), (o)--at a mutually-agreed upon price, and (q)
11.  Section 5(u)
12.  Section 6(a), (e) through (g)--except (g)(i)
13.  Section 6(k) will be amended to read in its entirety as follows:  "Allow
     Distributor to inspect Supplier's facilities during normal business hours
     in the event of a recall or field corrective action in order to allow
     Distributor to audit the operations and quality system elements associated
     with the affected Products and allow Distributor access to the device
     master and device history records for the affected Products."
14.  Section 6(m) through (o), (s), (t), (v)
15.  Section 6(aa)
16.  Section 7
17.  Section 10
18.  Section 11
19.  Section 12
20.  Section 13(a)
21.  Section 13(c) through (i), (n), (o), (r)
22.  Section 14
23.  The first and last sentences of Section 15
24.  Section 16
25.  Section 17
26.  Sections II.C, II.D and II.F of Exhibit C to the Second Amendment to this
     Agreement, as modified by the February Letter Agreement and the March
     Letter Agreement
26.  All Exhibits and Schedules, to the extent referenced in the above-specified
     text
27.  The February Letter Agreement, March Letter Agreement and April Letter
     Agreement

                                      -44-
<PAGE>

                                                                      Schedule 2
                                                                      ----------

                 Terms of Distribution Agreement (as amended)
                 to be Operative at the Effective Time of the
                      Termination of the Agency Agreement
              (any items not listed herein will not be operative)

1.   Section 1 (Definitions)
2.   Section 2(a)(3), although the lead-in language of 2(a) will be amended to
     read in its entirety as follows:  "Supplier hereby grants to Distributor
     the non-exclusive right to sell the Hemostasis and MicroScan classes of
     Products throughout the Territory, subject to the following conditions and
     limitations"
3.   Section 2(b)(2) and (3)
4.   Section 2(c) (although the notices from Distributor specified at the end
     thereof will no longer be necessary)
5.   Section 3 will be amended to read in its entirety as follows: "The term of
     this agreement shall begin at the effective time of the termination of the
     Agency Agreement between Distributor and Supplier (the "Agency Agreement"),
     and shall end on the later of (i) the date that there is no remaining Net
     Book Value on any Valid Active AdNow Lease that was originally subject to
     the Agency Agreement and (ii) the date which is nine months after the
     effective time of the termination of the Agency Agreement."
6.   Section 4
7.   Section 5(a) will be amended to read in its entirety as follows: "Supply
     Products to existing customers pursuant to all Valid Active AdNow Leases
     and Valid Inactive AdNow Leases then in existence that were originally
     subject to the Agency Agreement."
8.   Section 5(b) and (c)
9.   Section 5(e)(1), (2), (3), (4); however, both the lead-in language and the
     unnumbered last paragraph of 5(e) are deleted
10.  Section 5(e)(12) (but only for those Valid Active AdNow Leases and Valid
     Inactive AdNow Leases then in existence that were originally subject to the
     Agency Agreement)
11.  Section 5(f)
12.  The first two sentences of Section 5(j)
13.  Section 5(m), (n), (o) - at a mutually-agreed upon price, and (q)
14.  Section 5(u)
15.  Section 6(a), (e) through (g)
16.  Section 6(k) will be amended to read in its entirety as follows:  "Allow
     Distributor to inspect Supplier's facilities during normal business hours
     in the event of a recall or field corrective action in order to allow
     Distributor to audit the operations and quality system elements associated
     with the affected Products and allow Distributor access to the device
     master and device history records for the affected Products."
17.  Section 6(m) through (o), (s), (t), (v)
18.  Section 6(aa)
19.  Section 7
20.  Section 8(a)(v) and (vi) and 8(e)
21.  Section 10
22.  Section 11
23.  Section 12
24.  Section 13(a)
25.  Section 13(b) shall be amended to read in its entirety as follows: "This
     Agreement, together with all amendments hereto, including without
     limitation the March Letter Agreement, the April Letter Agreement, and the
     February Letter Agreement, constitute the entire agreement between the
     parties with respect to the subject matter hereof and shall supersede all
     previous negotiations, commitments and writings with respect to such
     subject matter."
26.  Section 13(c) through (i), (n), (o), (r)
27.  Section 14
28.  The first and last sentences of Section 15
29.  Section 16
30.  Section 17
31.  Exhibit A shall be amended so that Distributor's guaranteed gross profit
     margins shall be 3%
32.  All other Exhibits and Schedules, to the extent referenced in the above-
     specified text
33.  The February Letter Agreement, March Letter Agreement and April Letter
     Agreement

                                      -45-