<PAGE>   1

                                                                  EXHIBIT-10.2

                             THE PIONEER GROUP, INC.

                                CREDIT AGREEMENT

                                 Amendment No. 6

     This Agreement, dated as of September 30, 1998, is among The Pioneer Group,
Inc., a Delaware corporation (the "Company"), certain of its subsidiaries listed
on the signature pages hereto, the Lenders (as defined in the Credit Agreement
referenced below) and BankBoston, N.A., f/k/a The First National Bank of Boston,
as agent (the "Agent") for itself and the other Lenders. The parties agree as
follows:

1. REFERENCE TO CREDIT AGREEMENT; DEFINITIONS. Reference is made to the Credit
Agreement dated as of June 6, 1996, among the Company, certain of its
subsidiaries, the Lenders and the Agent (as amended, modified and in effect
prior to giving effect to this Agreement, the "Credit Agreement"). Terms defined
in the Credit Agreement as amended hereby (the "Amended Credit Agreement") and
not otherwise defined herein are used herein with the meanings so defined.
Except as the context otherwise explicitly requires, the capitalized terms
"Section" and "Exhibit" refer to sections hereof and exhibits hereto.

2. AMENDMENTS TO CREDIT AGREEMENT. Subject to all of the terms and conditions
hereof and in reliance upon the representations and warranties set forth in
Section 3, the Credit Agreement is amended as follows, effective upon the date
(the "Amendment Date") that the conditions specified in Section 4 are satisfied,
which conditions must be satisfied no later than September 30, 1998 or this
Agreement shall be of no force or effect:

     1. ADDITION OF SECTION 1.13A. A new Section 1.13A is added to the Credit
Agreement immediately after Section 1.13 of the Credit Agreement to read in its
entirety as follows:

          "1.13A "B SHARE PURCHASE DOCUMENTS" means, collectively, the (a)
     Pioneer Program Master Agreement, dated as of September 30, 1998, by and
     among the Company, Pioneering Management Corporation (the "Advisor"),
     Pioneer Funds Distributor, Inc. (the "Distributor"), PLT Finance, L.P. (the
     "Purchaser"), Putnam, Lovell, de Guardiola & Thornton Inc. (the "Program
     Administrator") and Bankers Trust Company as collection agent (the
     "Collection Agent"); (b) the Pioneer Program Purchase Agreement, dated as
     of September 30, 1998, by and between the Distributor and the Purchaser;
     (c) the Pioneer Program Funding and Collection Agency Agreement, dated as
     of September 30, 1998, by and among the Collection Agent, the Purchaser,
     the Program Administrator and the Distributor; (d) the Pioneer Program
     Servicer Agent Agreement, dated as of September 30, 1998, by and among the
     Purchaser, the Program Administrator and the Distributor as program
     servicer agent; and all other instruments, documents and agreements
     executed by the Company or its 

<PAGE>   2
     Subsidiaries in connection with the
     foregoing, to be entered into for the purpose of generating net proceeds
     sufficient to prepay all of the Credit Obligations with respect to the B
     Share Term Loan."

     2. AMENDMENT OF SECTION 1.113A. A new Section 1.113A is added to the Credit
Agreement immediately after Section 1.113 of the Credit Agreement to read in its
entirety as follows:

          "1.113A. "PORTFOLIO ASSETS" means with respect to each applicable
     Fund, all of the rights under the related Distribution Agreement, the
     related Distribution Plan and the related prospectus to receive amounts
     paid or payable in respect of Distribution Fees (including interest) and
     Contingent Deferred Sales Charges, in each case in respect of the B Shares
     of such Fund and in respect of B Shares of any other Fund acquired in any
     permitted free exchange of B Shares of the Fund in question, including any
     similar amount paid or payable under any replacement distribution plan,
     distribution agreement or prospectus, and any continuation payments in
     respect thereof paid or payable by the related Trust in respect of the B
     Shares of such Fund in the event of a termination of the related
     Distribution Plan, Distribution Agreement or prospectus."

     3. AMENDMENT OF SECTION 4.3. Section 4.3 of the Credit Agreement is amended
to read in its entirety as follows:

     "4.3. MANDATORY PREPAYMENT OF B SHARE TERM LOAN.

               4.3.1. Until all of the Credit Obligations with respect to the B
          Share Term Loan are paid in full pursuant to Section 4.3.2 and in
          addition to any amounts paid in accordance with Section 4.2, the
          Borrower Subsidiaries will, as a mandatory prepayment of the B Share
          Term Loan, pay to the Agent for the Lenders' accounts on each Payment
          Date, commencing on the last Banking Day of the first full calendar
          quarter after the B Share Conversion Date, an amount equal to the
          greater of (i) 5% of the B Shares Term Loan outstanding on the B Share
          Conversion Date or (ii) the B Share Collection Amount for the quarter
          ending on such Payment Date; provided that the amount of any such
          prepayment shall not exceed the amount of the B Share Term Loan
          outstanding at the time of such prepayment.

               4.3.2. In addition to any amounts paid in accordance with
          Sections 4.2 and 4.3.1, the Borrower Subsidiaries will, as a mandatory
          prepayment of the B Share Term Loan, pay to the Agent for the Lenders'
          accounts on the earlier of (a) twenty-one Banking Days after the date
          of the consummation of the transactions contemplated by the B Share
          Purchase Documents or (b) three Banking Days after the receipt by the
          Company or any of its Subsidiaries of proceeds from the sale of the
          Portfolio Assets permitted in clause (a) of Section


                                      -2-
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          7.11.6, the full amount of the Credit Obligations with respect to the
          B Share Term Loan outstanding as of such date out of the proceeds of
          the sale of the Portfolio Assets permitted in clause (a) of Section
          7.11.6."

     4. AMENDMENT OF SECTION 7.11. Section 7.11 of the Credit Agreement is
amended by adding a new Section 7.11.6 immediately after 7.11.5 of the Credit
Agreement to read in its entirety as follows:

          "7.11.6. Pursuant to the B Share Purchase Documents, the Company and
     its Subsidiaries may sell, transfer, convey and assign to PLT Finance, L.P.
     or its Affiliates the right, title and interest in, to and under all
     Portfolio Assets to be conveyed, arising directly and indirectly out of all
     applicable B Shares of each applicable Fund, the date of issuance of which
     B Shares is (a) before September [30], 1998 or (b) during the period from
     the date on which the transactions contemplated by the B Share Purchase
     Documents are consummated through the third anniversary of such date;
     PROVIDED that immediately before and after giving effect to any such sale,
     transfer, conveyance or assignment no Default exists; PROVIDED, FURTHER,
     that the proceeds of the sale permitted in clause (a) of this Section
     7.11.6 shall be used to prepay the B Share Term Loan as required by Section
     4.3.2."

3. REPRESENTATIONS AND WARRANTIES. In order to induce the Lenders to enter into
this Agreement, the Company represents and warrants to each of the Lenders that:

     1. LEGAL EXISTENCE, ORGANIZATION. Each of the Company and its Subsidiaries
is duly organized and validly existing and in good standing under the laws of
the jurisdiction of its incorporation, with all power and authority, corporate
or otherwise, necessary to (i) enter into and perform this Agreement, the
Amended Credit Agreement and each other Credit Document to which it is party and
(ii) own its properties and carry on the business now conducted or proposed to
be conducted by it. Each of the Company and its Subsidiaries has taken, or shall
have taken on or prior to the Amendment Date, all corporate or other action
required to make the provisions of this Agreement, the Amended Credit Agreement
and each other Credit Document to which it is party the valid and enforceable
obligations they purport to be.

     2. ENFORCEABILITY. The Company and each of its Subsidiaries which are
signatories hereto have duly executed and delivered this Agreement. Each of this
Agreement and the Amended Credit Agreement is the legal, valid and binding
obligation of the Company and such Subsidiaries and is enforceable in accordance
with its terms.

     3. NO LEGAL OBSTACLE TO AGREEMENTS. Neither the execution, delivery or
performance of this Agreement, nor the performance of the Amended Credit
Agreement, nor the consummation of any other transaction referred to in or
contemplated by this Agreement, 


                                      -3-


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nor the fulfillment of the terms hereof or thereof, has constituted or resulted
in or will constitute or result in:

          (1) any breach or termination of the provisions of any agreement,
     instrument, deed or lease to which the Company or any Subsidiary is a party
     or by which it is bound, or of the Charter or Bylaws of the Company or any
     Subsidiary;

          (2) the violation of any law, judgment, decree or governmental order,
     rule or regulation applicable to the Company or any Subsidiary;

          (3) the creation under any agreement, instrument, deed or lease of any
     Lien upon any of the assets of the Company or any Subsidiary; or

          (4) any redemption, retirement or other repurchase obligation of the
     Company or any Subsidiary under any Charter, By-law, agreement, instrument,
     deed or lease.

No approval, authorization or other action by, or declaration to or filing with,
any governmental or administrative authority or any other Person is required to
be obtained or made by the Company or any Subsidiary in connection with the
execution, delivery and performance of this Agreement or the performance of the
Amended Credit Agreement, or the consummation of the transactions contemplated
hereby or thereby.

     4. NO DEFAULT. Immediately before and after giving effect to the amendments
set forth in Section 2, no Default will exist.

     5. INCORPORATION OF REPRESENTATIONS AND WARRANTIES. The representations and
warranties set forth in Section 8 of the Credit Agreement are true and correct
on the date hereof as if originally made on and as of the date hereof (except to
the extent any representation or warranty refers to a specific earlier date).

4. CONDITIONS. The effectiveness of this Agreement shall be subject to the
satisfaction of the following conditions:

     1. OFFICER'S CERTIFICATE. The representations and warranties contained in
Section 3 shall be true and correct as of the Amendment Date with the same force
and effect as though originally made on and as of such date; no Default shall
exist on the Amendment Date prior to or immediately after giving effect to this
Agreement; as of the Amendment Date, no Material Adverse Change shall have
occurred; and the Company shall have furnished to the Agent on the Amendment
Date a certificate to these effects, in substantially the form of Exhibit 4(a),
signed by an Executive Officer or a Financial Officer.


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     2. PAYMENT OF LEGAL FEES. The Borrower shall have paid the reasonable fees
and disbursements of Ropes & Gray, special counsel to the Lenders, outstanding
as of the Amendment Date.

     3. PROPER PROCEEDINGS. All proper corporate proceedings shall have been
taken by each of the Company and the Subsidiaries to authorize this Agreement,
the Amended Credit Agreement and the transactions contemplated hereby and
thereby. The Agent shall have received copies of all documents, including legal
opinions of counsel and records of corporate proceedings which the Agent may
have requested in connection therewith, such documents, where appropriate, to be
certified by proper corporate or governmental authorities.

     4. EXECUTION BY LENDERS. Each of the Lenders shall have executed and
delivered this Agreement to the Company.

5. FURTHER ASSURANCES. Each of the Company and the Subsidiaries will, promptly
upon request of the Agent from time to time, execute, acknowledge and deliver,
and file and record, all such instruments and notices, and take all such action,
as the Agent deems necessary or advisable to carry out the intent and purposes
of this Agreement.

6. GENERAL. The Amended Credit Agreement and all of the other Credit Documents
are each confirmed as being in full force and effect. This Agreement, the
Amended Credit Agreement and the other Credit Documents referred to herein or
therein constitute the entire understanding of the parties with respect to the
subject matter hereof and thereof and supersede all prior and current
understandings and agreements, whether written or oral, with respect to such
subject matter. The invalidity or unenforceability of any provision hereof shall
not affect the validity or enforceability of any other term or provision hereof.
The headings in this Agreement are for convenience of reference only and shall
not alter, limit or otherwise affect the meaning hereof. Each of this Agreement
and the Amended Credit Agreement is a Credit Document and may be executed in any
number of counterparts, which together shall constitute one instrument, and
shall bind and inure to the benefit of the parties and their respective
successors and assigns, including as such successors and assigns all holders of
any Note. THIS AGREEMENT SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH
THE LAWS (OTHER THAN THE CONFLICT OF LAWS RULES) OF THE COMMONWEALTH OF
MASSACHUSETTS.


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Each of the undersigned has caused this Agreement to be executed and delivered
by its duly authorized officer as an agreement under seal as of the date first
above written.

THE PIONEER GROUP, INC.                 PIONEERING SERVICES CORPORATION  
                                                                         
                                                                         
By /s/ William H. Keough                 By /s/ William H. Keough          
  ----------------------                   ----------------------          
  Title: Treasurer                         Title: Treasurer             
                                                                         
60 State Street                         60 State Street                  
Boston, Massachusetts 02109-1820        Boston, Massachusetts 02109-1820 
                                        

PIONEERING MANAGEMENT
CORPORATION


By /s/ William H. Keough
  ---------------------- 
  Title: Treasurer

60 State Street
Boston, Massachusetts 02109-1820


PIONEER MANAGEMENT (IRELAND) 
LTD.


By John F. Cogan, Jr.
  ------------------
  Title: Director

60 State Street
Boston, Massachusetts 02109-1820


PIONEER FUNDS DISTRIBUTOR, INC.


By /s/ William H. Keough
  ----------------------
  Title: Treasurer

60 State Street
Boston, Massachusetts 02109-1820



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                    BANKBOSTON, N.A.                       
                                                           
                                                           
                    By /s/ Stewart P. Neff                 
                      --------------------                 
                      Title: Managing Director             
                                                           
                      Financial Institutions Division      
                      100 Federal Street - 15th Floor      
                      Boston, Massachusetts 02110          
                      Telecopy: (617) 434-1537             
                      Telex:  940581                       
                                                           
                                                           
                    THE BANK OF NEW YORK                   
                                                           
                                                           
                    By   Jean A. Mahony                    
                      -----------------                    
                    Title: Asst. Vice President            
                                                           
                    One Wall Street, 17th Floor            
                    Mutual Fund Banking Division           
                    New York, NY  10286                    
                    Telecopy:  (212) 635-6348              
                    Telex:                                 
                                                           
                                                           
                    SOCIETE GENERALE                       
                                                           
                                                           
                    By /s/ Woody Littlefield               
                      ----------------------               
                    Title: Vice President                  
                                                           
                    1221 Avenue of the Americas            
                    New York, New York 10020               
                    Telecopy: (212) 278-7153               
                                                           
                    
                                      -7-

<PAGE>   8


                    STATE STREET BANK & TRUST COMPANY                         
                                                                              
                                                                              
                    By: /s/ Michael St. Jean                                  
                       ---------------------                                  
                    Title: Vice President                                     
                                                                              
                    225 Franklin Street, 8th Floor                            
                    Asset-Based Finance                                       
                    Boston, MA 02110                                          
                    Telecopy: (617) 338-4041                                  
                                                                              
                                                                              
                    BANQUE NATIONALE DE PARIS                                 
                                                                              
                                                                              
                    By: /s/ Laurent Vanderzyppe        Marguerite L. Lebon    
                       ------------------------        -------------------    
                       Title:  Vice President          Asst. Vice President   
                                                                              
                    499 Park Avenue, 2nd Floor                                
                    New York, 10022                                           
                    Telecopy: (212) 415-9707                                  
                                                                              
                                                                              
                    MELLON BANK, N.A.                                         
                                                                              
                                                                              
                    By: John Cooper                                           
                       -------------                                          
                       Title:  Vice President                                 
                                                                              
                    One Mellon Bank Center                                    
                    Mail Code: 1510370                                        
                    Pittsburgh, PA 15258                                      
                    Telecopy: (412) 234-8087                                  
                    

                                      -8-


<PAGE>   9


                                                                    EXHIBIT 4(a)

                              OFFICER'S CERTIFICATE

     Pursuant to Section 4(a) of Amendment No. 6 to Credit Agreement dated as of
September 30, 1998 (the "Amendment") among The Pioneer Group, Inc., a Delaware
corporation (the "Company"), certain of its subsidiaries signatories thereto,
the Lenders and BankBoston, N.A., f/k/a The First National Bank of Boston, as
agent (the "Agent") for itself and the other Lenders, which amends the Credit
Agreement dated as of June 6, 1996 (as amended, modified and in effect prior to
giving effect to the Amendment, the "Credit Agreement"), among the Company,
certain of its subsidiaries signatories thereto, the Lenders and the Agent, the
Company hereby certifies that the representations and warranties contained in
Section 3 of the Amendment are true and correct on and as of the Amendment Date
with the same force and effect as though originally made on and as of the
Amendment Date; no Default exists on the Amendment Date or will exist
immediately after giving effect to the Amendment; and as of the Amendment Date,
no Material Adverse Change has occurred.

     Terms defined in the Amendment and not otherwise defined herein are used
herein with the meanings so defined.

     This certificate has been executed by a duly authorized Executive Officer
or Financial Officer this 30th day of September, 1998.

                                THE PIONEER GROUP, INC.

                                By /s/ William H. Keough      
                                  ----------------------   
                                  Name: William H. Keough 
                                  Title: Treasurer