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                                FOURTH AMENDMENT
                                       TO
                    REVOLVING CREDIT AGREEMENT (UNGUARANTEED)
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         Fourth  Amendment  dated  as of  March  31,  2000 to  Revolving  Credit
Agreement  (the  "Fourth  Amendment"),  by and among  APPNET  SYSTEMS,  INC.,  a
Delaware  corporation (the  "Borrower"),  FLEET NATIONAL BANK (formerly known as
BANKBOSTON, N.A.) and the other lending institutions listed on Schedule 1 to the
Credit  Agreement (as  hereinafter  defined)  (the  "Banks"),  amending  certain
provisions of the  Revolving  Credit  Agreement  dated as of January 8, 1999 (as
amended and in effect from time to time,  the "Credit  Agreement")  by and among
the Borrower,  the Banks,  Fleet  National Bank  (formerly  known as BankBoston,
N.A.) as agent for the Banks (the "Agent") and Antares  Capital  Corporation  as
co-agent for the Banks.  Terms not otherwise defined herein which are defined in
the Credit Agreement shall have the same respective meanings herein as therein.

         WHEREAS, the Borrower and the Banks have agreed to modify certain terms
and conditions of the Credit  Agreement as specifically set forth in this Fourth
Amendment;

         NOW,  THEREFORE,  in  consideration  of the  premises  and  the  mutual
agreements contained herein and for other good and valuable  consideration,  the
receipt and  sufficiency  of which are hereby  acknowledged,  the parties hereto
hereby agree as follows:

         ss.1. Amendment to Section 1.1 of the Credit Agreement.  The definition
of "EBITDA"  contained in ss.1.1 of the Credit  Agreement  is hereby  amended by
deleting such definition in its entirety and restating it as follows:

                  EBITDA. With respect to the Borrower and its Subsidiaries
         for any fiscal period,  an amount equal to Consolidated Net Income
         for such period,  plus, to the extent  deducted in the calculation
         of Consolidated Net Income and without duplication, (a) income tax
         expense for such period;  (b) Consolidated  Total Interest Expense
         paid or accrued  (excluding  accrued interest the payment of which
         is  deferred  beyond  one year from the date such  amount is being
         determined)  during such period; (c) depreciation and amortization
         for such period;  (d) the one-time  expense incurred in the fiscal
         quarter  ended  September  30, 1999  pertaining  to the  severance
         arrangements  for certain  employees;  (e) the one-time charge for
         bad debts taken in the fiscal  quarter  ended March 31, 2000 in an
         aggregate  amount not to exceed  $3,400,000  and (f) the amount of
         any  earn-out  or  noncompete  for such  period to the extent such
         amount was  capitalized  and  treated as debt  (including  without
         limitation  any  earn-out  such  as  that  which  was  part of the
         consideration  in the acquisition of New Media  Publishing,  Inc.,
         which  earn-out was

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                                    -2-


         accounted for as compensation and noncompete and capitalized as an
         intangible asset and amortized), and minus, to the extent added in
         computing  Consolidated  Net Income and without  duplication,  all
         noncash gains (including income tax benefits) for such period, all
         as determined in accordance  with  generally  accepted  accounting
         principles.

         ss.2.  Conditions to  Effectiveness.  This Fourth  Amendment  shall not
become  effective  until  the  Agent  receives  a  counterpart  of  this  Fourth
Amendment, executed by the Borrower, each Subsidiary and the Banks

         ss.3.  Representations  and Warranties.  The Borrower hereby represents
that, on and as of the date hereof,  each of the  representations and warranties
made by it in ss.7 of the Credit  Agreement  remain  true as of the date  hereof
(except to the extent of changes  resulting from  transactions  contemplated  or
permitted  by the Credit  Agreement  and the other Loan  Documents  and  changes
occurring in the ordinary course of business that singly or in the aggregate are
not  materially  adverse,  and to  the  extent  that  such  representations  and
warranties relate expressly to an earlier date),  provided,  that all references
therein to the Credit  Agreement shall refer to such Credit Agreement as amended
hereby.  In  addition,  the Borrower  hereby  represents  and warrants  that the
execution  and  delivery by the  Borrower  and its  Subsidiaries  of this Fourth
Amendment and the performance by the Borrower and its Subsidiaries of all of its
agreements  and  obligations  under the  Credit  Agreement  and the  other  Loan
Documents as amended  hereby are within the  corporate  authority of each of the
Borrower and its  Subsidiaries  and has been duly  authorized  by all  necessary
corporate action on the part of the Borrower and its Subsidiaries.

         ss.4. Ratification, Etc. Except as expressly amended hereby, the Credit
Agreement  and  all  documents,  instruments  and  agreements  related  thereto,
including,  but not limited to the Security  Documents,  are hereby ratified and
confirmed  in all  respects  and shall  continue in full force and  effect.  The
Credit  Agreement  and this Fourth  Amendment  shall be read and  construed as a
single  agreement.  All  references  in the  Credit  Agreement  or  any  related
agreement or instrument to the Credit  Agreement  shall  hereafter  refer to the
Credit Agreement as amended hereby.

         ss.5. No Waiver. Nothing contained herein shall constitute a waiver of,
impair or otherwise affect any Obligations, any other obligation of the Borrower
or any rights of the Agent or the Banks consequent thereon.

         ss.6.  Counterparts.  This Fourth  Amendment  may be executed in one or
more counterparts,  each of which shall be deemed an original but which together
shall constitute one and the same instrument.

         ss.7.  Governing Law. THIS FOURTH  AMENDMENT  SHALL BE GOVERNED BY, AND
CONSTRUED IN ACCORDANCE  WITH,  THE LAWS OF THE  COMMONWEALTH  OF  MASSACHUSETTS
(WITHOUT REFERENCE TO CONFLICT OF LAWS).

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         IN WITNESS  WHEREOF,  the  parties  hereto  have  executed  this Fourth
Amendment as a document under seal as of the date first above written.

                                        APPNET SYSTEMS, INC.



                                        By: /s/
                                           ------------------------------------
                                        Title:

                                        FLEET NATIONAL BANK (formerly
                                        know as BankBoston, N.A.)



                                        By: /s/
                                           ------------------------------------
                                           Jay L. Massimo, Director


                                        ANTARES CAPITAL CORPORATION



                                        By: /s/
                                           ------------------------------------
                                        Title:

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                                      -4-


                            RATIFICATION OF GUARANTY

         Each of the undersigned  guarantors hereby acknowledges and consents to
the foregoing  Fourth Amendment as of March 31, 2000 and agrees that each of the
Guaranty dated as of January 8, 1999, March 4, 1999 and March 10, 1999 from each
of the undersigned  guarantors remains in full force and effect, and each of the
guarantors confirms and ratifies all of its obligations thereunder.

                                        APPNET OF MICHIGAN, INC.



                                        By: /s/
                                           ------------------------------------
                                        Title:

                                        APPNET OF MARYLAND, INC.



                                        By: /s/
                                           ------------------------------------
                                        Title:


                                        SOFTWARE SERVICES CORPORATION



                                        By: /s/
                                           ------------------------------------
                                        Title:


                                        NEW MEDIA PUBLISHING, INC.



                                        By: /s/
                                           ------------------------------------
                                        Title:


                                        RESEARCH & PLANNING, INC.


                                        By: /s/
                                           ------------------------------------
                                        Title:
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                                      -5-


                                        CENTURY COMPUTING, INCORPORATED



                                        By: /s/
                                           ------------------------------------
                                        Title:


                                        THE KODIAK GROUP, INC.



                                        By: /s/
                                           ------------------------------------
                                        Title:


                                        I33 COMMUNICATION CORP.



                                        By: /s/
                                           ------------------------------------
                                        Title:


                                        SIGMA6, INC.



                                        By: /s/
                                           ------------------------------------
                                        Title:


                                        SALZINGER ACQUISITION CORP.



                                        By: /s/
                                           ------------------------------------
                                        Title: