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                     Firstar Agrees to Acquire Mercantile,
                 Creating $75 Billion Midwest Banking Franchise

 Transaction to Provide 8.5 Percent EPS Accretion in 1999, 10.7 Percent in 2000

MILWAUKEE and ST. LOUIS, April 30, 1999--Firstar Corporation
(NYSE:FSR) today announced that it has signed a definitive agreement to
acquire Mercantile Bancorporation Inc. (NYSE:MTL) through an exchange of
shares valued at approximately $10.6 billion.

Under the terms of the agreement, Mercantile shareholders will receive a
tax-free exchange of 2.091 shares of Firstar common stock for each share of
Mercantile common stock owned. Based on Firstar's closing stock price on April
29, 1999 (the date the exchange rate was finalized) this represents a price of
$66.00 for each Mercantile share, a premium of 29 percent over Mercantile's
closing price of $51.25 per share on that date, and a multiple of 21.6 times
Mercantile's 1999 estimated earnings per share.

This transaction will create 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 1,180 branch locations in nine Midwest states and
Tennessee, Arkansas and Arizona, plus trust operations in Florida. The combined
company would become the 13th largest bank holding company in the United States,
with assets of more than $75 billion, deposits of $59 billion, assets under
management of $67 billion and a market capitalization of $32 billion.

After the closing, the combined company expects to pay dividends at an annual
rate of $0.65 per common share. This approximates a continuation of the current
$1.36 dividend rate paid on Mercantile shares, adjusted for the exchange ratio.
This dividend rate would represent an increase of 63 percent on the current
$0.40 annual dividend rate paid on Firstar shares. The combined companies'
corporate headquarters will remain in Milwaukee, with St. Louis becoming the
headquarters for corporate banking and Cincinnati continuing as the headquarters
for consumer banking.

Jerry A. 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, will become
chairman of the board of Firstar and will co-chair the board's executive
committee with Grundhofer. Roger L. Fitzsimonds, Firstar's current chairman,
plans to retire upon the closing of the acquisition and will be 



named chairman emeritus at that time. The board of directors will be comprised 
of 14 representatives of Firstar and four representatives of Mercantile.

"We are announcing today the combination of two excellent banks with long and
distinguished histories, outstanding people, and superior potential for future
growth," said Grundhofer. "Together, we will create a preeminent Midwest
franchise in financial services. By combining our franchises we will continue to
build critical mass in our key business lines, with emphasis on sales, customer
service and strong industry-leading technology. We will be a rapidly growing,
very profitable, highly efficient organization with a continued strong
commitment to community involvement. This merger will provide enhanced benefits
for our customers, our employees and our communities, as well as, unmatched
economic benefits for shareholders of both companies."

"Combining with Firstar is a uniquely attractive strategic opportunity for
Mercantile," said Jacobsen, "not only for the economic benefits it offers our
shareholders, but also for the continuity of quality customer service and
community involvement for St. Louis, Kansas City and our entire banking
franchise. Firstar has proven that it can combine a highly effective operating
style with strong local market involvement. We are delighted to be combining
with a bank whose priorities are so completely compatible with our own. Each of
us has products, skills and resources to bring to the other. We look forward to
a seamless integration of our two companies into a single regional banking
leader."

The transaction will be accounted for as a pooling of interests, and is expected
to close in the fourth quarter of 1999. It is expected to be 8.5 percent
accretive to Firstar's earnings per share in 1999, and 10.7 percent accretive in
2000. This accretion is based on anticipated expense reductions, and does not
include earnings from revenue enhancements or the reinvestment of excess
capital. Firstar expects to incur pre-tax merger-related and restructuring
charges of $428 million between the closing of the transaction and the end of
2000.

Firstar and Mercantile estimate that they will reduce their expenses by $169
million, with 100 percent of these savings to be achieved in 2000. These cost
savings represent 19 percent of Mercantile's current expense base, and would
bring the combined company into line with Firstar's current efficiency ratio.
The cost saving opportunities include centralization of corporate activities,
consolidation of data processing and operations, optimization of commercial
banking, retail branches and alternative delivery channels for bank products and
services, improvements in technology, and reconfiguration of mortgage, credit
card and asset management businesses. Systems conversion will begin after year
end and continue throughout the year 2000.

Additionally, the companies believe there is significant opportunity for future
revenue growth resulting from product cross-selling, accelerated consumer loan
growth, new product introductions, and increased scale in key business lines,
including consumer, commercial and small business lending, asset management,
mortgage banking, correspondent banking and cash management. Customers of the
combined company will have access to approximately 1180 branches, the nation's
seventh-largest system and more than 2000 ATM's, the tenth-largest system and a
broad range of electronic banking, 



PC banking and Internet banking products and services. The combined company will
rank in the top five in share of deposits in Missouri, Iowa, Wisconsin, 
Kentucky, Minnesota, Arkansas, Ohio, Illinois, and Kansas, and also have a 
presence in Indiana, Tennessee, Arizona and Florida.

Firstar's highly successful incentive-based compensation program, known as "Pay
for Performance" will be implemented throughout the combined company. This
program provides all employees with incentive pay linked to individual
performance and selected measures of shareholder value creation. Also, Firstar
is the only bank in the country to guarantee its quality customer service with
its unique "Five Star Service Guarantee" in all lines of business.

"It is essential today that when companies combine, they do so seamlessly," said
Jacobsen. "We are heartened by the speed and smoothness of the recent Star
Banc-Firstar merger; combined with our own experience in post-transaction
integration, it leads us to believe that together we can minimize near-term
disruptions as we create our region's premier banking institution. The
compatibility of our cultures will facilitate the process, and the scale and
growth of the resulting organization will create new opportunities for all our
people."

"The strongest banks grow from deep local roots. Firstar has consciously
nurtured its links to its core markets, and we intend to bring this same sense
of nurture to the deep ties that Mercantile has developed over many decades in
St. Louis, and other important markets in Missouri, Arkansas, Kansas, Iowa,
Illinois and Kentucky," said Grundhofer. "It is important to note that
throughout Firstar, today and in the future, all our business lines will have a
strong local presence, with local decision-making authority. We will continue to
maintain key processing and mortgage production centers in St. Louis. In
addition to our business activities and our local market involvement, we will
continue Mercantile's impressive community commitments. I will be spending the
majority of my time in St. Louis for the foreseeable future, and Tom and I look
forward to meeting with leaders of the community to discuss how we can best
preserve and enhance the citizenship role Mercantile has long played in the
community."

The transaction, which was approved by the boards of both companies, is subject
to normal shareholder and regulatory approvals. Both companies have completed
due diligence, including Year 2000 compliance issues. In connection with the
merger agreement, Firstar and Mercantile have each granted the other
cross-options to purchase common shares of the other company under certain
circumstances.

Firstar was advised in this transaction by the investment bank of Credit
Suisse/First Boston. The investment bank of Donaldson, Lufkin & Jenrette
provided a fairness opinion and acted as financial advisor to Mercantile. Morgan
Stanley Dean Witter also rendered a fairness opinion to Mercantile.

Firstar Corporation is a $38 billion bank holding company with approximately 720
full-service banking offices in Ohio, Wisconsin, Kentucky, Illinois, Indiana,
Iowa, Minnesota, Tennessee and Arizona. 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.

Mercantile is a $36 billion multi-bank holding company headquartered in St.
Louis, which operates banks in nearly 500 locations in Missouri, Iowa, Kansas,
Illinois, Arkansas and Kentucky. Mercantile's non-banking subsidiaries include
companies providing brokerage services, asset-based lending, factoring, 
investment advisory services, leasing services and credit life and other 
insurance products as agent.

                                      ###

This news release contains forward looking statements with respect to the
financial condition, results of operations and business of Firstar and
Mercantile and assuming the consummation of the merger, a combined Firstar and
Mercantile, including statements relating to: the cost savings and revenue
enhancements and accretion to reported earnings that will be realized from the
merger; and the restructuring charges expected to be incurred in connection with
the merger. These forward looking statements involve certain risks and
uncertainties. Factors that may cause actual results to differ materially from
those contemplated by such forward looking statements include, among other
things, the following possibilities: expected cost savings from the merger
cannot be fully realized or realized within the expected time; revenues
following the merger are lower than expected; competitive pressure among
depository institutions increases significantly; costs of the difficulties
related to the integration of the business of Firstar and Mercantile are greater
than expected; changes in the interest rate environment reduce interest margins;
general economic conditions, either nationally or in the states in which the
combined company will be doing business, are less favorable than expected;
legislation or regulatory requirements or changes adversely affect the business
in which the combined company will be engaged; and changes may occur in the
securities market. All dividends on Firstar common stock are subject to
determination by the Firstar board of directors in its discretion.