Firstar Corporation and Mercantile Bancorporation Merger Completed

MILWAUKEE and ST. LOUIS--(BUSINESS  WIRE)--Sept. 20, 1999--The merger of Firstar
Corporation  (NYSE:FSR - news) and Mercantile  Bancorporation  Inc.  (NYSE:MTL -
news) was officially completed this morning at 12:01 a.m. EDT, Monday, September
20, 1999. The combined  companies will now be called "Firstar  Corporation"  and
its common  stock will  trade on the New York  Stock  Exchange  under the ticker
symbol "FSR." This announcement was made by Jerry A. Grundhofer, president and
chief executive officer of Firstar Corporation.

This transaction creates the second largest Midwest banking franchise, providing
a full line of consumer  banking,  commercial  banking and trust and  investment
management  services and products to more than 5 million  customers  through its
approximately  1,200  branch  locations in nine  Midwest  states and  Tennessee,
Arkansas, Florida and Arizona. The combined company will become the 14th largest
bank holding company in the United States, with assets of more than $74 billion.

Grundhofer  commented,  "We are pleased to welcome  Firstar's newest  customers,
employees  and  shareholders  to our  organization.  The  merging  of these  two
first-class  banks  creates a leading  provider  of  financial  services  in the
Midwest region, with the ability to offer greater financial strength,  a broader
range of products and services,  stronger  technology and greater  efficiency to
our customers and communities.  This merger provides unmatched economic benefits
for shareholders and will position Firstar strategically to operate on a new and
higher level of banking going forward.  In the coming months, we look forward to
introducing  our new  customers in St. Louis,  Kansas City and Little Rock,  and
those in other important markets in Missouri,  Kansas,  Arkansas, Iowa, Illinois
and  Kentucky,  to  Firstar.  We are  excited  about being able to offer our new
customers  our Five Star Service  Guarantee,  24-Hour  Banking  System and other
industry-leading financial services and products available at Firstar."

Firstar's corporate  headquarters remain in Milwaukee,  with St. Louis being the
headquarters  for  corporate  banking and  Cincinnati,  Ohio,  continuing as the
headquarters  for  consumer  banking.  In  addition  to  "guaranteed   service,"
customers of Firstar will now have access to  approximately  1,200  full-service
branch locations, more than 2,000 ATM's, a broad range of electronic banking, PC
banking and Internet banking products and services.

Grundhofer,  Firstar's  president and chief executive officer,  will continue in
that position.  Thomas H. Jacobsen,  Mercantile's chairman,  president and chief
executive officer,  who will be based in St. Louis, is now chairman of the board
of Firstar and will co-chair the board's  executive  committee with  Grundhofer.
Roger L. Fitzsimonds,  Firstar's current chairman, has announced plans to retire
and has been named chairman emeritus.  Firstar Corporation's board of directors,
which includes  Grundhofer and Jacobsen,  is comprised of the following members:
Victoria B. Buyniski,  John C. Dannemiller,  David B. Garvin, J. P. Hayden, Jr.,
Roger L. Howe, David B. O'Maley,  O'dell M. Owens, M.D., Thomas E. Petry, Joe F.
Hladky, Sheldon B. Lubar, Daniel F. McKeithan, Jr., John J. Stollenwerk, William
W. Wirtz, Frank Lyon, Jr., Craig D. Schnuck and Patrick T. Stokes.

Firstar   Corporation   will  be  a  $74  billion  bank  holding   company  with
approximately 1,200 full-service banking offices in Ohio,  Wisconsin,  Missouri,
Kentucky,  Iowa, Illinois,  Kansas,  Indiana,  Arkansas,  Minnesota,  Tennessee,
Arizona  and  Florida.  Firstar  offers a full  complement  of  banking,  trust,
investment,  insurance,  securities  brokerage  and  other  financial  services.
Firstar Corporation is the parent company of Firstar Finance, a consumer finance
company and Firstar Investment Research & Management Company,  LLC (FIRMCO),  an
investment advisory firm. Visit Firstar on the web at  www.firstar.com.  Firstar
was founded in 1853.

Contact:

     Firstar Corporation
     Steve Dale (Media), 414/765-4455
     Joe Messinger (Analysts), 414/765-5235