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                                                                   EXHIBIT 10.18

                           FIFTH AMENDMENT AGREEMENT
                           -------------------------

     FIFTH AMENDMENT AGREEMENT (this "Amendment Agreement") dated as of April
30, 1999- by and among Moore Medical Corp. (the "Borrower"), BankBoston, N.A.
(as successor by merger to Bank of Boston Connecticut) and certain other lending
institutions (collectively, the "Banks"), and BankBoston, N.A. (as successor by
merger to Bank of Boston Connecticut), as agent for the Banks (in such capacity,
the "Agent"), amending a certain Revolving Credit Agreement dated as of January
9, 1996, as amended by the First Amendment Agreement dated as of March 1, 1996,
the Second Amendment Agreement dated as of December 27, 1996, the Third
Amendment and Waiver Agreement dated as of April 14, 1997 and the Fourth
Amendment and Waiver Agreement dated as of March 30, 1998 (as amended, the
"Credit Agreement").


                                  WITNESSETH
                                  -----------
     WHEREAS, the Borrower has requested that the Banks amend certain terms and
conditions of the Credit Agreement; and

     WHEREAS, the Banks and the Agent are willing to amend such terms and
conditions on the terms and conditions set forth herein.

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

     (S)1.  Definitions. Capitalized terms used herein without definition that
            -----------
are defined in the Credit Agreement shall have the same meanings herein as
therein.

     (S)2.  Ratification of Existing Agreements. All of the Borrower's
            -----------------------------------
obligations and liabilities to the Agent and the Banks, and all the Agent's and
Banks' obligations and liabilities to the Borrower, as evidenced by or otherwise
arising under the Credit Agreement, the Notes and the other Loan Documents,
except as otherwise expressly modified in this Amendment Agreement upon the
terms set forth herein, are, by the Borrower's, the Agent's and Banks',
execution of this Amendment Agreement ratified and confirmed in all respects. In
addition, by the Borrower's execution of this Amendment Agreement, the Borrower
represents and warrants that, subject to the provided and provided, however,
clauses of Section 5.4 of the Credit Agreement, no counterclaim, right of
set-off or defense of any kind exists or is outstanding with respect to such
obligations and liabilities.

     (S)3.  Representations and Warranties. All of the representations and
            ------------------------------
warranties made by the Borrower in the Credit Agreement, the Notes and the other
Loan Documents are true and correct on the date hereof as if made on and as of
the date hereof, except to the extent that any of such representations and
warranties relate by their terms to a prior date and except to the extent of
changes resulting from transactions contemplated or permitted by the Credit
Agreement and

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changes occurring in the ordinary course of business that singly or in the
aggregate do not have a Material Adverse Effect.

     (S)4.  Conditions Precedent. The effectiveness of the amendments
            --------------------
contemplated hereby shall be subject to the satisfaction on or before the date
hereof of each of the following conditions precedent:

             (a)  Representations and Warranties. All of the representations and
                  ------------------------------
     warranties made by the Borrower herein, whether directly or incorporated by
     reference, shall be true and correct on the date hereof, except as provided
     in (S)3 hereof.

             (b)  Performance: No Event of Default. The Borrower shall have
                  --------------------------------
     performed and complied in all material respects with all terms and
     conditions herein required to be performed or complied with by it prior to
     or at the time hereof, and there shall exist no Default or Event of
     Default.

             (c)  Corporate Action. All requisite corporate action necessary for
                  ----------------
     the valid execution, delivery and performance by the Borrower of this
     Amendment Agreement and all other instruments and documents delivered by
     the Borrower in connection therewith shall have been duly and effectively
     taken.

             (d)  Delivery. The parties hereto shall have executed and delivered
                  --------
     this Amendment Agreement. In addition, the Borrower shall have executed and
     delivered such further instruments, and take such further action as the
     Agent and the Banks may have reasonably requested, in each case further to
     effect the purposes of this Amendment Agreement, the Credit Agreement and
     the other Loan Documents.

             (e)  Fees and Expenses. The Borrower shall have paid to the Agent
                  -----------------
     and the Banks all fees and expenses incurred by the Agent in connection
     with this Amendment Agreement, the Credit Agreement or the other Loan
     Documents on or prior to the date hereof.

     (S)5.  Amendments to Credit Agreement.
            ------------------------------

             (S)5.1. Amendment to (S) 2.1. Section 2.1 of the Credit Agreement
                     --------------------
     is hereby amended by deleting the entire thirteenth line of such section
     and substituting the phrase "time exceed the Total Commitment." therefor.

             (S)5.2. Amendment to (S) 2.10.  Section 2.10 of the Credit
                     ---------------------
     Agreement is hereby deleted in its entirety.

             (S)5.3. Amendment to (S) 3.2. Section 3.2 of the Credit Agreement
                     --------------------
     is hereby amended by deleting the phrase "lesser of (a) the Total
     Commitment and (b) the Borrowing Base." in the fourth line thereof and
     substituting the phrase "the Total Commitment," therefor.

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             (S)5.4.   Amendment to (S) 4.1. Section 4.1(a) of the Credit
                       --------------------
     Agreement is hereby amended by deleting the phrase "lessor of (1) the Total
     Commitment and (2) the Borrowing Base." in the second to last and last line
     thereof and substituting the phrase "Total Commitment." therefor.

             (S)5.5.   Amendment to (S) 6. Section 6 of the Credit Agreement is
                       ------------------
     hereby amended in its entirety to read as follows:

             "(S)6.    Intentionally Omitted."

             (S)5.6.   Amendment to (S) 7.14.  Section 7.14 of the Credit
                       ---------------------
     Agreement is hereby amended in its entirety to read as follows:

             "(S)7.14. Intentionally Omitted."

             (S)5.7.   Amendment to (S) 8.4. Section 8.4(e) of the Credit
                       -------------------
     Agreement is hereby amended in its entirety to read as follows:

             "(e)        intentionally omitted;"

             (S)5.8.   Amendment to (S)8.5. Clause "(ii)" of Section 8.5(b) of
                       -------------------
     the Credit Agreement is hereby amended in its entirety to read as follows:

             "(ii)  upon becoming aware thereof, of any inquiry, proceeding,
     investigation, or other action, including a notice from any agency of
     potential environmental liability, or any federal, state or local
     environmental agency or board, that has the potential to materially affect
     the assets, liabilities, financial conditions or operations of the Borrower
     or any of its Subsidiaries."

             (S)5.9.   Amendment to (S)8.5.  Section 8.5(c) of the Credit
                       -------------------
     Agreement is hereby amended in its entirety to read as follows:

             "(c)       Notification of Claim Against Assets. The Borrower will,
     immediately upon becoming aware thereof, notify the Agent and each of the
     Banks in writing of any setoff, claims (including, with respect to the Real
     Estate, environmental claims), withholdings or other defenses to which any
     of the assets of the Borrower, or the Agent's rights with respect thereto,
     are subject."

             (S)5.10.  Amendment to (S)8.7. Section 8.7 of the Credit Agreement
                       -------------------
     is hereby amended in its entirety to read as follows:

             "(S)8.7.  Insurance The Borrower will, and will cause each of its
                       ---------
     Subsidiaries to, maintain with financially sound and reputable insurers
     insurance with respect to its properties and business against such
     casualties and contingencies as shall be in accordance with the general
     practices of businesses engaged in similar activities in similar geographic
     areas and in amounts, containing such terms, in such forms and for such
     periods as may be reasonable and prudent."

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          (S)5.11.  Amendment to (S) 8.13. Section 8.13 of the Credit Agreement
                    ---------------------
     is hereby deleted.

          (S)5.12.  Amendment to (S) 9.1. Section 9.1 of the Credit Agreement
                    --------------------
     is hereby amended by deleting "." from the end of subsection "(h)" and
     substituting "; and" therefore and by adding a new subsection "(i)" to such
     section to read as follows:

          "(i) Indebtedness in the aggregate principal amount not in excess of
     $10,000,000 at any time as long as such Indebtedness is either (x)
     unsecured or (y) incurred in connection with the acquisition of Acquired
     Assets or Capitalized Leases and is secured only by such Acquired Assets or
     such Capitalized Leases with no other recourse of any kind whatsoever to
     the Borrower,"

          (S)5.13.  Amendment to (S) 9.2. Section 9.2(e)(viii) of the Credit
                    --------------------
     Agreement is hereby amended by adding the phrase "Acquired Assets or" after
     the phrase "mortgages on" in the second line of such section and adding the
     phrase "or (S)9.1(i)(y)" after "(S)9.1(f)" in the fifth line of such
     section.

          (S)5.14.  Amendment to (S) 9.3. Section 9.3 of the Credit Agreement
                    ---------------------
     is hereby amended by deleting "." from the end of subsection "(i)" and
     substituting "; and" therefore and by adding a new subsection "(j)" to such
     section to read as follows:

          "(j)       the Permitted Acquisitions."

          (S)5.15.  Amendment to (S) 9.5. Section 9.5(a) of the Credit Agreement
                    --------------------
     is hereby amended by inserting the phrase "the Permitted Acquisitions or"
     after the phrase "other than" in the fourth line of such section.

          (S)5.16.  Amendment to (S) 10.5. Section 10.5 of the Credit Agreement
                    ---------------------
     is amended by adding the phrase "(other than for Capital Assets acquired in
     connection with Permitted Acquisitions)" after the phrase "Capital
     Expenditures" in the second line of such section.

          (S)5.17.  Amendment to (S) 11.  Section 11.5 of the Credit Agreement
                    -------------------
       is hereby amended in its entirety to read as follows:

          "(S)11.5  Intentionally Omitted."

          (S)5.18.  Amendment to (S) 12.3. Section 12.3 of the Credit Agreement
                    --------------------
       is hereby amended in its entirety to read as follows:

          "(S)12.3. Intentionally omitted."

          (S)5.19.  Amendment to (S) 13.1.  Section 13.1(m) of the Credit
                    ---------------------
     Agreement is hereby amended in its entirety to read as follows:

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          "(m) there shall occur any material damage to, or loss, theft or
     destruction of, any assets of the Borrower, or any strike, lockout, labor
     dispute, embargo, condemnation, act of God or public enemy, or other
     casualty, which in any such case causes, for more than fifteen (15)
     consecutive days, the cessation or substantial curtailment of revenue
     producing activities at any facility of the Borrower or any of its
     Subsidiaries if such event or circumstance is not covered by business
     interruption insurance and would have a Materially Adverse Effect."

          (S)5.20.   Amendment to (S) 13.1.  Section 13.1(o) of the Credit
                     --------------------
     Agreement is hereby amended in its entirety to read as follows:

          "(o)        the Borrower or any of its Subsidiaries shall be indicted
     for a federal crime, a punishment for which could include the forfeiture of
     any assets of the Borrower or such Subsidiary having a fair market value in
     excess of $1,000,000;"

          (S)5.21.   Amendment to (S) 13.4. The first paragraph of Section 13.4
                     ---------------------
     of the Credit Agreement is hereby amended in its entirety to read as
     follows:

          "(S)13.4   Distribution of Proceeds. In the event that following the
                     ------------------------
     occurrence or during the continuance of any Default or Event of Default,
     the Agent or any Bank, as the case may be, receives any monies in
     connection with the enforcement of any the Loan Documents, or otherwise
     with respect to the realization upon any of the assets of the Borrower,
     such monies shall be distributed for application as follows:"

          (S)5.22.   Amendment to (S) 13.4. Section 13.4(a) of the Credit
                     ---------------------
     Agreement is hereby amended by deleting the word "Collateral" in the
     seventh line thereof and substituting the phrase "assets of the Borrower"
     therefor.

          (S)5.23.   Amendment to (S) 14. Section 14 of the Credit Agreement is
                     -------------------
     hereby amended by deleting the word "Collateral," in the first line thereof
     and substituting the phrase "collateral security, if any," therefor.

          (S)5.24.   Amendment to (S)15.11.  Section 15.11 of the Credit
                     ---------------------
     Agreement is hereby amended in its entirety to read as follows:

          "(S)15.11. Duties in the Case of Enforcement. In case one of more
                     ---------------------------------
          Events of Default have occurred and shall be continuing, and whether
          or not acceleration of the Obligations shall have occurred, the Agent
          shall, if (a) so requested by the Majority Banks and (b) the Banks
          have provided to the Agent such additional indemnities and assurances
          against expenses and liabilities as the Agent may reasonably request,
          proceed to enforce the provisions of the Loan Documents authorizing
          the sale or other disposition of all or any part of the assets of the
          Borrower and exercise all or any such other legal and equitable and
          other rights or remedies as it may have in respect of such assets. The
          Majority Banks may direct the Agent in writing as to the method and
          the extent of any such sale or other disposition, the Banks hereby
          agreeing to indemnify and hold the Agent, harmless

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          from all liabilities incurred in respect of all actions taken or
          omitted in accordance with such directions, provided that the Agent
                                                      --------
          need not comply with any such direction to the extent that the Agent
          reasonably believes the Agent's compliance with such direction to be
          unlawful or commercially unreasonable in any applicable jurisdiction."

          (S)5.25. Amendment to (S) 16. Section 16 of the Credit Agreement is
                   -------------------
     hereby amended by deleting the word "Collateral;" in the fourth to last
     line thereof and substituting the phrase "collateral security;" therefor.

          (S)5.26. Amendment to (S) 17. Section 17 of the Credit Agreement is
     hereby amended by deleting the word "Collateral," in the fourteenth line
     thereof and substituting the phrase "assets of the Borrower," therefor.

          (S)5.27. Amendments to Schedule 2. Schedule 2 is hereby amended by
                   ------------------------
     deleting the definitions of "Borrowing Base," "Borrowing Base Report,"
     "Collateral," "Perfection Certificates" and "Security Agreement" set forth
     therein.

          (S)5.28. Amendments to Schedule 2.
                   ------------------------

                    (a)  The definition of "Loan Documents" appearing in
     Schedule 2 to the Credit Agreement is hereby amended by deleting the phrase
     "Security Agreement" from the second line thereof.

                    (b)  The following definitions of "Permitted Acquisitions"
     and "Acquired Assets" are hereby added to Schedule 2 to the Credit
     Agreement in the proper alphabetical order to read as follows:

                    "Permitted Acquisitions. Shall mean any acquisition of all
                    -----------------------
     or substantially all the assets of, or shares or other equity interest in,
     a Person or division or line of business ("Acquired Assets") of a Person if
     immediately after giving effect thereto: (a) no Default or Event of Default
     shall have occurred and be continuing or would result therefrom, (b) all
     transactions related thereto shall be consummated in accordance in all
     material respects with applicable laws, (c) the Bank shall have received
     evidence that the board of directors (or Persons performing similar
     functions) of such Person shall have approved such acquisition, such
     evidence of approval to be in form and substance reasonably satisfactory to
     the Bank in all respects, (d) such acquisition is in the same or similar
     line of business of the Borrower, (e) the payment of the total
     consideration for such acquisition, separately and when considered with all
     acquisitions of Acquired Assets since the Closing Date, shall not be in
     excess of $10,000,000, (f) one hundred percent (100%) of the capital stock
     or other equity interest of any acquired or newly formed corporation,
     partnership, limited liability, association or other business entity is
     owned directly by the Borrower or a Subsidiary of the Borrower and (g)(x)
     the Borrower and its Subsidiaries shall be in compliance, on a pro forma
     basis after giving effect to such acquisition or formation, with the
     covenants contained in (S)10 recomputed as at the last day of each relevant
     period for testing such compliance, and the Borrower shall have

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     delivered to the Bank an officer's certificate to such effect, together
     with all relevant financial information for such subsidiary or assets, and
     (y) any acquired or newly formed subsidiary shall not be liable for any
     Indebtedness (except for Indebtedness permitted by (S)9.1 hereof).

          (S)6.  Release of Collateral. Subject to the satisfaction of the
                 ---------------------
     conditions set forth herein and in accordance with the terms hereof, the
     Banks and the Agent hereby release the security interest in and lien on the
     Collateral and agree to execute and file termination statements in all
     filing offices of each jurisdiction in which a financing statement with
     respect to any of the Collateral was filed, all at the cost and expense of
     the Borrower.

          (S)7.  Expenses. The Borrower agrees to pay to the Agent upon demand
                 --------
     an amount equal to any and all out-of-pocket costs or expenses (including
     reasonable legal fees and disbursements and appraisal expenses) incurred or
     sustained by the Agent in connection with the preparation of this Amendment
     Agreement and any related matters.

          (S)8.  Miscellaneous.
                 -------------

                  (c)  This Amendment Agreement shall be governed by and
     construed in accordance with the laws of the State of Connecticut.

                  (d)  Except as otherwise expressly provided by this Amendment
     Agreement, all of the respective terms, conditions and provisions of the
     Credit Agreement shall remain the same and in full force and effect. It is
     declared and agreed by each of the parties hereto that this Amendment
     Agreement and the Credit Agreement be read and construed as one instrument,
     and all referenced in the Loan Documents to the Credit Agreement shall
     hereafter refer to the Credit Agreement, as amended by this Amendment
     Agreement.

     IN WITNESS WHEREOF, each of the parties hereto have caused this Amendment
Agreement to be executed in its name and behalf by its duly authorized officer
as of the date first written above.

                                   MOORE MEDICAL CORP.


                                   By:  /s/ David V. Harper
                                        -------------------
                                        Executive Vice President - Finance and
                                        Chief Financial Officer

                                   BANKBOSTON, N.A. (as successor by merger to
                                   Bank of Boston Connecticut) Individually and
                                   as Agent


                                   By:  /s/ Donald W. Peters
                                        --------------------
                                        Vice President

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