Exhibit 2.3
                            AGREEMENT OF AFFILIATES
                            -----------------------


     THIS AGREEMENT OF AFFILIATES (the "Agreement") is made as of January 14,
1998, between the undersigned officers, directors and stockholders (the
"Affiliates") of Heritage Financial Services, Inc. ("Heritage"), and First
Midwest Bancorp, Inc. ("Acquiror"), for the purpose of inducing Acquiror and
First Midwest Acquisition Corporation to enter into an Agreement and Plan of
Merger (the "Merger Agreement") with Heritage.  Capitalized terms used in this
Agreement, and not otherwise defined, have the meanings ascribed to them in the
Merger Agreement.

     1.   So long as the Merger Agreement has not been terminated, in
consideration of the Merger, the parties agree as follows:

     (a)  Each Affiliate, as an individual, shall use all reasonable efforts to
          cause the Merger Agreement to be adopted by the shareholders of
          Heritage and consummated according to its terms.

     (b)  Each Affiliate agrees to cause all shares of capital stock of Heritage
          ("Heritage Shares") owned by him or her or with respect to which he or
          she shall have the sole right to vote, and to use all reasonable
          efforts to cause shares with respect to which he or she shall share
          the right to vote, to be voted in favor of the approval of the Merger
          and the adoption of the Merger Agreement; provided, however, that this
          provision shall not apply to any Heritage Shares held by an Affiliate
          as a trustee or in any other comparable fiduciary capacity.

     (c)  Each Affiliate agrees that until the Merger is consummated or
          abandoned pursuant to the Merger Agreement, he or she shall not,
          without Acquiror's written consent, voluntarily sell or dispose of any
          Heritage Shares owned or controlled by him or her or solicit, invite,
          negotiate, discuss or enter into any agreement concerning any
          Acquisition Transaction. Acquiror's written consent shall not be
          unreasonably withheld in the event of a disposition by gift to a
          charity or to a family member of the Affiliate made for estate
          planning purposes and not to avoid the restrictions hereof, or in the
          event of a disposition necessary to discharge a fiduciary duty as a
          trustee or comparable fiduciary capacity; provided such transferee
          agrees to be bound by the terms and conditions of this Agreement.

     2.   This Agreement may be executed in multiple counterparts at different
times by Acquiror and different Affiliates, each of which shall be an original,
but all of which together constitute one and the same agreement.  This
Agreement, including each of its counterparts, shall be effective with respect
to additional Affiliates as, when, and if executed by Acquiror and such
additional Affiliates.  Neither Acquiror's nor any Affiliate's rights or
obligations under this Agreement 

 
are contingent upon the execution of this Agreement by any other Affiliate and
this Agreement shall be binding only with respect to each signatory to this
Agreement and any of its counterparts.

     3.   This Agreement sets forth the entire agreement and understanding
between Acquiror and the Affiliates in respect of the transactions contemplated
by this Agreement and supersedes all prior agreements, arrangements, and
understandings relating to the subject matter hereof.

     4.   This Agreement shall continue in effect until the Merger is
consummated or the Agreement is terminated in accordance with its terms.

     IN WITNESS WHEREFORE, each of the undersigned Affiliates has executed this
Agreement in his or her individual capacity as of the date first written above.

RICHARD T. WOJCIK                   FREDERICK J. SAMPIAS
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Richard T. Wojcik                   Frederick J. Sampias                        
                                                                                
RONALD P. GROCBE                    JOHN T. GALLAGHER                           
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Ronald P. Grocbe                    John T. Gallagher                           
                                                                                
LEAL W. MATHIS                      JACK PAYAN                                  
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Lael W. Mathis                      Jack Payan                                  
                                                                                
ARTHUR E. SIELOFF                   JOHN L. STERLING                            
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Arthur E. Sieloff                   John L. Sterling                            
                                                                                
CHESTER STRANCZEK                   ARTHUR G. TICHENOR                          
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Chester Stranczek                   Arthur G. Tichenor                          
                                                                                
DOMINICK J. VELO                    JOHN E. BARRY                               
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Dominick J. Velo                    John E. Barry

PAUL A. ECKROTH
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Paul A. Eckroth                     Carl C. Greer, individually and as President
                                    of Martin Marketing and as Voting Trustee
                                    under a Voting Trust Agreement, dated
                                    December 31, 1985, as amended on December
                                    31, 1995

                                    FIRST MIDWEST BANCORP, INC.
 
                                           DONALD J. SWISTOWICZ
                                    By:----------------------------------------
                                             Its Executive Vice President

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