<PAGE>   1
                                                                    EXHIBIT 10.5



                             THE PIONEER GROUP, INC.

                                CREDIT AGREEMENT

                                 Amendment No. 1
                                 ---------------

     This Agreement, dated as of April 23, 1997, 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 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, (the "Credit Agreement"), among the Company,
certain of its subsidiaries, the Lenders and the Agent. 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 April 24, 1997 or this
Agreement shall be of no force or effect:

     2.1. AMENDMENT TO SECTION 1.9. Section 1.9 of the Credit Agreement is
amended to read in its entirety as follows:

          "1.9. "B SHARE CONVERSION DATE" means the earlier of April 22, 1998 or
     such later date as determined in accordance with Section 2.2.3."

     2.2. AMENDMENT TO SECTION 1.124. Section 1.124 of the Credit Agreement is
amended to read in its entirety as follows:

          "1.124. "STATED MAXIMUM AMOUNT OF B SHARE REVOLVING CREDIT" means the
     lesser of (i) $60,000,000 or such lesser amount to which the lending
     commitment of the Lenders may be reduced pursuant to Section 4, and (ii)
     such amount (in a minimum amount of $10,000,000 and an integral multiple of
     $1,000,000) less than the Maximum Amount of B Share Revolving Credit then
     in effect as specified by irrevocable notice from the Company to the
     Agent."

     2.3. AMENDMENT TO EXHIBIT 11.1. Exhibit 11.1 of the Credit Agreement is
amended as provided on Exhibit 2.2 hereto.


<PAGE>   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:

     3.1. 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 (a) enter into and perform this Agreement,
the Amended Credit Agreement and each other Credit Document to which it is party
and (b) 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.

     3.2. ENFORCEABILITY. The Company and each of its subsidiaries which are
signatories hereto has 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.

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

          (a) 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 By-laws of the Company or any
     Subsidiary;

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

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

          (d) 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.

                                       -2-

  

<PAGE>   3




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

     3.5. INCORPORATION OF REPRESENTATIONS AND WARRANTIES. The representations
and warranties set forth in Section 8 of the Amended 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:

     4.1. 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 4.1,
signed by an Executive Officer or a Financial Officer.

     4.2. 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.

     4.3. 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

                                       -3-
 

<PAGE>   4




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.








                                       -4-

   

<PAGE>   5




     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 CORP.



By  /s/ William H. Keough                    By  /s/ William H. Keough
    ------------------------------               -----------------------------
    Title: Senior Vice President                 Title: Treasurer
           Chief Financial Officer
           & 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  /s/ John F. Lawlor               
    ------------------------------ 
    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





                                      -4-


<PAGE>   6




                                   THE FIRST NATIONAL BANK OF BOSTON

                                   By  /s/ Stewart 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  /s/ 
                                       ---------------------------------
                                       Title: Vice President

                                       One Wall Street, OWS-1 
                                       Securities Industry Division 
                                       New York, NY 10286 
                                       Telecopy: (212) 809-9566 
                                       Telex:



                                   SOCIETE GENERALE

                                   By  /s/ D.E. Littefield
                                       ---------------------------------
                                       Title: Vice President and Manager

                                       1221 Avenue of the Americas
                                       New York, New York 10020
                                       Telecopy: (212) 278-7153
  

        

                                       -5-

<PAGE>   7


                                   STATE STREET BANK & TRUST COMPANY

                                   By  /s/ 
                                       --------------------------------
                                       Title: Vice President

                                       225 Franklin Street, 8th Floor
                                       Asset-Based Finance
                                       Boston, MA 02110
                                       Telecopy: (617) 338-4041



                                   BANQUE NATIONALE DE PARIS

                                   By  /s/ William Shaheen
                                       --------------------------------
                                       Title: Vice President


                                   By  /s/ Laurent Vanderzyppe
                                       --------------------------------
                                       Title: Assistant Vice President

                                       499 Park Avenue, 7th Floor 
                                       New York, 10022 
                                       Telecopy: (212) 415-9707



                                   MELLON BANK, N.A.

                                   By  /s/ Susan M. Whitewood
                                       --------------------------------
                                       Title: Assistant Vice President

                                       One Mellon Bank Center 
                                       Mail Code: 1510370 
                                       Pittsburgh, PA 15258 
                                       Telecopy: (412) 234-8087



                                       -6-


<PAGE>   8

                                                                     Exhibit 2.2
                                                                     -----------


<TABLE>

                              PERCENTAGE INTERESTS
---------------------------------------------------------------------------------------------------------------
<CAPTION>
Lender                 Total Commitment       B Share Loan          Revolving Loan          Percentage Interest
------                 ----------------       ------------          --------------          -------------------
<S>                    <C>                    <C>                   <C>                     <C>
The First National     $36,521,739.15         $15,652,173.93        $20,869,565.22          26.087%
Bank of Boston
---------------------------------------------------------------------------------------------------------------
Mellon Bank, N.A.      $30,434,782.61         $13,043,478.26        $17,391,304.35          21.739%
---------------------------------------------------------------------------------------------------------------
State Street Bank &    $24,347,826.09         $10,434,782.61        $13,913,043.48          17.391%
Trust Company
---------------------------------------------------------------------------------------------------------------
The Bank of New        $18,260,869.56         $ 7,826,086.95        $10,434,782.61          13.043%
York
---------------------------------------------------------------------------------------------------------------
Societe Generale       $18,260,869.56         $ 7,826,086.95        $10,434,782.61          13.043%
---------------------------------------------------------------------------------------------------------------
Banque Nationale       $12,173,913.04         $ 5,217,391.30        $ 6,956,521.74           8.696%
de Paris
---------------------------------------------------------------------------------------------------------------
TOTAL                 $140,000,000.00         $60,000,000.00        $80,000,000.00         100.000%
---------------------------------------------------------------------------------------------------------------
</TABLE>



                                      -8-
<PAGE>   9

                                                                     Exhibit 4.1
                                                                     -----------




                              OFFICER'S CERTIFICATE

     Pursuant to Section 4.1 of Amendment No. 1 to Credit Agreement dated as of
April __, 1997 (the "Amendment") among The Pioneer Group, Inc., a Delaware
corporation (the "Company"), certain of its subsidiaries signatories thereto,
the Lenders and 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 (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 _____ day of April, 1997.

                                        THE PIONEER GROUP, INC.

                                        By 
                                           ------------------------------
                                           Name: 
                                           Title: