<PAGE>

                                                                EXHIBIT 10.16.3



                       THIRD AMENDMENT TO CREDIT AGREEMENT


      THIS THIRD AMENDMENT TO CREDIT AGREEMENT made and entered into as of June
___, 2000, by and among PSYCH SYSTEMS HOLDINGS, INC., a Delaware corporation
(the "COMPANY"), AMERICAN PSYCH SYSTEMS HOLDINGS, INC., a Delaware corporation
(the "HOLDING COMPANY"), the Lenders signatory hereto (the "LENDERS"), and BANC
OF AMERICA COMMERCIAL FINANCE CORPORATION, formerly known as NationsCredit
Commercial Corporation, as Agent for the Lenders (the "AGENT").

                               STATEMENT OF FACTS

      A. The Company, the Holding Company, the Lenders and the Agent are parties
to that certain Credit Agreement, dated as of December 23, 1998, as amended by
the First Amendment dated August 26, 1999 and the Second Amendment dated as of
October 18, 1999 (the "CREDIT AGREEMENT"; capitalized terms used in this
Amendment and not otherwise defined herein have the meanings given in the Credit
Agreement), whereby the Lenders have agreed to make certain loans to the
Company, subject to the terms and conditions contained in the Credit Agreement.

      B. The Company has requested that the Agent and the Lenders modify the
Credit Agreement in certain respects, and the Agent and the Lenders are willing
to agree to such modifications, subject to the terms and conditions of this
Amendment.

                               STATEMENT OF TERMS

      1.    AMENDMENT TO CREDIT AGREEMENT. Subject to the terms and conditions
of this Amendment, Section 1.01 of the Credit Agreement is hereby amended by
replacing the definition of "LETTER OF CREDIT LIMIT" with the following
definition:

            "LETTER OF CREDIT LIMIT" means $1,050,000.

      2. REPRESENTATIONS AND WARRANTIES. Each of the Company and the Holding
Company hereby represents and warrants to the Agent and the Lenders that (a)
this Amendment has been duly authorized, executed and delivered by the Company
and the Holding Company, (b) no Default or Event of Default has occurred and is
continuing as of this date, and (c) all of the representations and warranties
made by each of the Company and the Holding Company in the Credit Agreement are
true and correct in all material respects on and as of the date of this
Amendment (except to the extent that any such representations or warranties
expressly referred to a specific prior date). Any breach by the Company or the
Holding Company of its representations and warranties contained in this Section
shall be an Event of Default for all purposes of the Credit Agreement.

      3. RATIFICATION. Each of the Company and the Holding Company hereby
ratifies and reaffirms each and every term, covenant and condition set forth in
the Credit Agreement and



                                       1
<PAGE>

all other documents delivered by each of the Company and the Holding Company in
connection therewith (including without limitation the other Financing Documents
to which each of the Company and the Holding Company is a party).

      4. ESTOPPEL. To induce the Agent and the Lenders to enter into this
Amendment, the Company hereby acknowledges and agrees that, as of the date
hereof, there exists no right of offset, defense or counterclaim in favor of the
Company as against the Agent or any Lender with respect to the obligations of
the Company to any of such parties under the Credit Agreement or the other
Financing Documents, either with or without giving effect to this Amendment.

      5. CONDITIONS TO EFFECTIVENESS. The Amendment contained in Section 1
shall become effective upon the date of this Amendment, subject to the
satisfaction of the following conditions on or prior to such date:

      (a) the receipt by the Agent of this Amendment, together with the Consent
      attached hereto, duly executed, completed and delivered by the Agent, the
      Lenders, the Company, the Holding Company, and the Subsidiaries;

      (b) receipt by the Agent of the fees and expenses due to its counsel from
      the Company; and

      (c) the receipt by the Agent of such other documents as the Agent may
      reasonably request.

      6. REIMBURSEMENT OF EXPENSES. The Company hereby agrees that it shall
reimburse the Agent and the Lenders on demand for all costs and expenses
(including without limitation attorney's fees) incurred by such parties in
connection with the negotiation, documentation and consummation of this
Amendment and the other documents executed in connection herewith and the
transactions contemplated hereby and thereby.

      7. GOVERNING LAW. THIS AMENDMENT SHALL BE GOVERNED BY AND CONSTRUED IN
ACCORDANCE WITH THE LAWS OF THE STATE OF GEORGIA WITHOUT REGARD TO ITS
PRINCIPLES OF CONFLICTS OF LAWS.

      8. SEVERABILITY OF PROVISIONS. Any provision of this Amendment which is
prohibited or unenforceable in any jurisdiction shall, as to such jurisdiction,
be ineffective to the extent of such prohibition or unenforceability without
invalidating the remaining provisions hereof or affecting the validity or
enforceability of such provision in any other jurisdiction. To the extent
permitted by applicable law, the Company and the Holding Company hereby waive
any provision of law that renders any provision hereof prohibited or
unenforceable in any respect.

      9. COUNTERPARTS. This Amendment may be executed in any number of
counterparts, all of which shall be deemed to constitute but one original and
shall be binding upon all parties, their successors and permitted assigns.


                                        2
<PAGE>

      10. ENTIRE AGREEMENT. The Credit Agreement as amended by this Amendment
embodies the entire agreement between the parties hereto relating to the subject
matter thereof and supersedes all prior agreements, representations and
understandings, if any, relating to the subject matter thereof.


                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]


                                       3

<PAGE>



IN WITNESS WHEREOF, the parties have caused this Amendment to be duly executed
by their respective officers, as of the date first above written.

                                    COMPANY:


                                    PSYCH SYSTEMS HOLDINGS, INC.


                                    By: /s/ Kenneth Kessler
                                       ---------------------------------
                                    Kenneth A. Kessler, M.D.
                                    President and Chief Executive Officer



                                    HOLDING COMPANY:


                                    AMERICAN PSYCH SYSTEMS
                                    HOLDINGS, INC.


                                    By: /s/ Kenneth Kessler
                                       ---------------------------------
                                    Kenneth A. Kessler, M.D.
                                    President and Chief Executive Officer




                                    LENDER AND AGENT:


                                    BANC OF AMERICA COMMERCIAL
                                    FINANCE CORPORATION, FORMERLY KNOWN AS
                                    NATIONSCREDIT COMMERCIAL CORPORATION


                                    By: /s/ Ronald S. Cohn
                                       ---------------------------------
                                    Ronald S. Cohn
                                    Authorized Signatory


                                       4

<PAGE>



                                     CONSENT

      The undersigned Credit Parties hereby acknowledge and consent to, and
agree to the terms of, the foregoing Third Amendment to Credit Agreement, and
ratify and confirm their respective obligations under the Financing Documents,
as of the date of the foregoing Third Amendment.

AMERICAN PSYCH SYSTEMS, INC.
AMERICAN PSYCH SYSTEMS OF PUERTO RICO, INC.
AMERICAN PSYCH SYSTEMS OF TEXAS, INC.
CH/ECP SYSTEMS, INC.
CHS MANAGED SERVICES, INC.
MANHATTAN PSYCH SYSTEMS, L.P.
       By: NEW YORK PSYCH SYSTEMS, INC., its General Partner
METROPOLITAN IPA, INC.
NEW YORK PSYCH SYSTEMS, INC.
NEW YORK PSYCH SYSTEMS, L.P.
       By: NEW YORK PSYCH SYSTEMS, INC., its General Partner
PSYCH SYSTEMS IPA, INC.
PSYCH SYSTEMS OF LONG ISLAND, INC.
PSYCH SYSTEMS OF MANHATTAN, INC.
PSYCH SYSTEMS OF WESTCHESTER, INC.
PSYCH SYSTEMS PPO, INC.
SUFFOLK PSYCH SYSTEMS, L.P.
       By: NEW YORK PSYCH SYSTEMS, INC., its General Partner
WESTCHESTER PSYCH SYSTEMS, L.P.
       By: NEW YORK PSYCH SYSTEMS, INC., its General Partner


By: /s/ Kenneth Kessler
    --------------------------------
Kenneth A. Kessler, M.D.
President and Chief Executive Officer


                                       5