EXHIBIT 99.1

                              FOR IMMEDIATE RELEASE


               SIS Bancorp, Inc. Announces Entry into Connecticut

Springfield,  MA - August 18,  1997;  8:30 a.m.,  The Boards of Directors of SIS
Bancorp,  Inc.  ("SIS"),  (NASDAQ:  SISB),  and Glastonbury Bank & Trust Company
("GBT"),  (NASDAQ:  GLBT),  announced  today that they have signed a  definitive
merger  agreement under which SIS will acquire all of the outstanding  shares of
GBT. As a result of the  transaction,  GBT will become a wholly owned subsidiary
of SIS.

The  transaction  is  structured  as a tax-free  exchange  of 0.74 shares of SIS
common stock for each of GBT's  1,829,920  shares of common stock.  Based on the
per share closing  price for SIS common stock on August 15, 1997 of $30.00,  the
transaction would be valued at $40.6 million and GBT shareholders  would receive
$22.20 in SIS common  stock for each share of GBT  common  stock.  At a purchase
price of $22.20 per share,  the exchange is  approximately  equivalent  to 2.26x
GBT's June 30, 1997 book value and approximately 16.3x GBT's annualized earnings
per share for the six months ended June 30, 1997. GBT has the right to terminate
the  agreement if SIS' average  stock price for the twenty  consecutive  trading
days  ending  on the  fifth  business  day  prior  to the  closing  date  of the
acquisition is below $25.00,  unless SIS agrees at such time to increase the per
share  exchange  ratio to ensure a per share value of $18.50 in SIS common stock
to GBT  stockholders.  In  connection  with  the  execution  of  the  definitive
agreement,   GBT  has  granted  SIS  an  option  to  purchase,   under   certain
circumstances,  approximately  8.5% of its authorized common stock. In the event
that such option becomes  exercisable,  GBT will be further  obligated to pay an
additional cash payment to SIS of $1.5 million.

The  transaction,  which will be  accounted  for as a pooling of  interests,  is
subject to approval by SIS and GBT shareholders and various regulatory agencies.
It is  anticipated  that the  transaction  will  close by year end  1997.  After
consummation  of the  transaction,  GBT  will  remain  a  Connecticut  chartered
commercial  bank led by J. Gilbert  Soucie,  GBT's  current  president and chief
executive  officer.  It is also  expected  that Mr.  Soucie  will  serve as vice
chairman  of SIS.  The Board of  Directors  of GBT will be  retained  to provide
continuing  leadership and guidance to the GBT  organization.  In addition,  SIS
will  increase the size of its Board of Directors to add one of GBT's  directors
to serve as a director of SIS after the merger is consummated.

In announcing  the  transaction,  F. William  Marshall,  Jr., SIS' president and
chief executive  officer stated,  "A partnership with Glastonbury Bank and Trust
demonstrates  SIS'  philosophy  towards the  importance  of  community  banking.
Expansion  into  Connecticut  has been one of our  strategic  objectives  and is
consistent with our ongoing efforts to increase  earnings and deliver a superior
return to our shareholders.  Central  Connecticut is a very attractive  consumer
and  commercial  banking market and is a natural,  contiguous  extension to SIS'
existing  banking  franchise.  GBT  provides a very solid base from which we can
together grow in this attractive market. Additionally, GBT's merchant processing
and insurance  businesses  will further expand and diversify the services we can
offer in the future."





SIS  expects to take a pre-tax  charge of $2.5  million in 1997 to cover  merger
related  expenses,  and expects the merger to have a positive impact on earnings
per share in 1998 and beyond.

J. Gilbert Soucie,  president and chief executive  officer of Glastonbury Bank &
Trust,  stated, "We are very pleased about the pending  affiliation with SIS, an
institution which shares our commitment to community banking. A partnership with
SIS will bring new technology, more products and services, and increased capital
to enhance GBT's abilities to serve its growing customer base. More importantly,
GBT will be able to  maintain  the same  strong  level of  personal  service and
community focus."

In  connection  with the  execution  of the merger  agreement,  the SIS Board of
Directors has rescinded its existing  authorization  to repurchase up to 286,180
shares of SIS common stock.  During 1997, SIS repurchased 146,400 shares, net of
shares  reissued  under SIS's  various  benefit  plans.

SIS Bancorp,  Inc.,  headquartered  in  Springfield,  MA, is the parent  holding
company of Springfield  Institution for Savings ("SlS Bank"),  a state chartered
savings bank. SIS Bank,  originally founded in 1827,  operates 24 branch banking
offices in Agawam,  Amherst,  Chicopee,  East Longmeadow,  Holyoke,  Longmeadow,
Ludlow, Northampton,  South Hadley, Springfield, West Springfield and Westfield,
MA. At June 30, 1997 SIS had total  assets of $1.4  billion,  total  deposits of
$1.0 billion, and total equity of $103.3 million.

Glastonbury  Bank & Trust  Company is a  Connecticut-state-chartered  commercial
bank  organized in 1919 and  headquartered  in  Glastonbury,  CT. GBT operates 8
branch  banking   offices  in  the   Connecticut   communities  of  Glastonbury,
Colchester,  East Hartford,  Portland, Rocky Hill and Wethersfield.  At June 30,
1997,  Glastonbury had total assets of $261.3 million,  total deposits of $216.6
million, and total equity of $18.0 million.

GBT  investor  inquiries  are to be  directed  to J.  Gilbert  Soucie  at  (860)
652-6500.  SIS  investor  inquiries  are to be  directed  to Ms.  Ting  Chang at
(413)748-8271. All media inquiries are to be directed to Ms. Kathleen Bourque at
(413)748-8243.

This news release contains certain forward looking statements regarding enhanced
revenues that may be realized from the  transaction.  SIS cautions  readers that
such  forward  looking  statements  involve  certain  risks  and  uncertainties,
including  a variety of factors  that may cause  SIS'  actual  results to differ
materially from the anticipated  results or other expectations  expressed in any
forward  looking  statements  made by, or on behalf of SIS.  These  factors  are
further detailed in SIS' current report on Form 8-K dated August 18, 1997, which
has been filed with the Securities and Exchange Commission.









                              Summary Information:

Acquisition Information

Exchange Ratio                                                   0.74

Glastonbury Shares Outstanding                                   1,829,920

New SIS Shares Issued                                            1,354,141

Valuation Based on Closing Price on August 15, 1997 of $30.00:

    Aggregate Purchase Price                                     $40.6 million
    Price Per Share                                              $22.20
    Price/Annualized Earnings Per Share
    for the six months ended June 30, 1997                       16.3x.
    Price/June 30,1997 Book Value                                2.26x.
    Core Deposit Premium                                         11%

Accounting Treatment                                             Pooling.

Expected Closing Date                                         Year end 1997.




Statistics at June 30, 1997 ($ Millions)                          SISB                       GLBT
- ----------------------------------------                          ----                       ----
                                                                                 

Headquarters                                               Springfield, MA               Glastonbury, CT

Branches                                                            24                         8

Assets                                                          $1,434.5                    $261.3

Net Loans                                                       $  645.9                    $152.9

Deposits                                                        $1,015.4                    $216.6

Equity                                                          $  103.3                    $ 18.0

Equity/Assets                                                        7.2%                      6.9%

Non-Performing Assets/Total Assets                                   0.47%                     1.04%

Loan Loss Reserves/Non-Performing Loans                            272%                      197%

Net Income for Six Months Ended June 30, 1997                   $    5.8                    $  1.2

FTE Employees                                                      483                       123