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                                                                   Exhibit 10.19

SIXTH AMENDMENT AGREEMENT
-------------------------

     SIXTH AMENDMENT AGREEMENT (This "Amendment Agreement") dated as of December
23, 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, the Fourth Amendment
and Waiver Agreement dated as of March 30, 1998 and the Fifth Amendment
Agreement dated as of April 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 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.
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            (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 instruments, and take such further action as the Agent and
     the Banks may have reasonably requested, in each case further to effect the
     purpose 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.  Amendment to Credit Agreement.
            -----------------------------

            (S)5.1. Amendment to Revolving Credit Loan Maturity Date. The
                    ------------------------------------------------
     definition of "Revolving Credit Loan Maturity Date" appearing in Schedule 2
     to the Credit Agreement, and as amended by the Second Amendment Agreement,
     is hereby further amended by deleting the date "December 31, 1999"
     appearing therein and substituting therefor the date "March 30, 2000".

     (S)6.  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)7.  Miscellaneous.
            -------------

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

            (b)  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 references in the Loan Documents to the Credit Agreement shall
     hereafter refer to the Credit Agreement, as amended by this Amendment
     Agreement.
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     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/ Joseph P. Savidge
                                       -----------------------
                                       Title: Senior 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
                                       ----------------------
                                       Title: Vice President