FILED PURSUANT TO RULE 425
                                                  Filer: UnionBanCal Corporation
                                                 Issuer: UnionBanCal Corporation
                                              Commission File Number:  001-15081


[UNIONBANCAL CORPORATION LOGO APPEARS HERE]                         NEWS RELEASE


FOR IMMEDIATE RELEASE (SEPTEMBER 26, 2003)

Union Bank Contact:      Joanne Curran 213-236-5017 (office) 213-503-9323 (cell)
                         Katie Madden  415-765-2617 (office) 415-264-2893 (cell)
Business Bancorp Contact:      Alan J. Lane (909) 888-2265

                       UNION BANK OF CALIFORNIA TO ACQUIRE
                           BUSINESS BANK OF CALIFORNIA

SAN FRANCISCO - UnionBanCal Corporation (NYSE: UB), parent company of Union Bank
of California,  N.A.,  jointly  announced today with Business  Bancorp  (NASDAQ:
BZBC),  parent  company  of  Business  Bank  of  California,  the  signing  of a
definitive  agreement  for Business  Bank of  California to be merged into Union
Bank of California in a transaction valued up to $134.9 million.

Business  Bank is a $660  million-asset  commercial  bank  headquartered  in San
Bernardino,   California,   with   approximately   235   employees  and  fifteen
full-service  branches in two distinct markets - the Southern  California Inland
Empire and the San Francisco Bay Area.  Business Bank's ten Southern  California
branches are located in the cities of Corona, Hemet, Hesperia,  Ontario, Phelan,
Redlands,  Riverside,  San Bernardino (2), and Upland.  Business Bank's five Bay
Area  branches are located in the cities of Hayward,  Petaluma,  San  Francisco,
South San Francisco, and San Rafael.

"We are committed to strengthening our presence in attractive California markets
and  this  acquisition  expands  our  franchise  in  some of  California's  most
desirable  markets," said Richard C.  Hartnack,  vice chairman of Union Bank and
head of community banking and investment services.  "Business Bank is a well-run
organization  that has a great  geographic fit with Union Bank's existing branch
network." The  acquisition  will expand Union Bank's  presence in the attractive
Inland Empire and San Francisco Bay Area markets.

"We are very  excited to  partner  with the  management  team and  employees  of
Business Bank," said Hartnack.  "Business  Bank's retail and business  customers
will be well served by our


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comprehensive  product offerings and commitment to superior  service."  Business
Bank's  customers  will be  offered  a wide  range of  additional  products  and
services,  including  property & casualty  insurance,  private  banking,  mutual
funds,  annuities,  trust services,  enhanced cash management and  international
banking services.

"The idea of partnering with one of California's top financial  institutions has
a strong  appeal to us. We are  enthusiastic  about our  merger  with Union Bank
because it makes sense for our shareholders,  customers,  and communities," said
Alan J. Lane, chief executive  officer of Business  Bancorp.  Lane added,  "This
merger will provide our customers with a broader array of financial products and
services while  maintaining the  community-oriented  philosophy that has made us
successful."

"We are excited about Union Bank's  commitment  to supporting  our community and
employees, and we are pleased with Union Bank's dedication to delivering quality
customer  service," said Charles O. Hall,  president of Business  Bancorp.  "Our
loyal customers are the reason Business Bank has enjoyed success over the years.
They will find that  Union  Bank is a company  that  shares  our  commitment  to
address the needs of the local residents of the communities it serves."

The  acquisition  reflects  Union Bank's  execution of its on-going  strategy to
expand its  branch-based  distribution  system.  The deal marks the fourth  bank
acquisition  for Union Bank since  2001,  following  the  acquisitions  of First
Western Bank, Valencia Bank & Trust, and Monterey Bay Bancorp.

The  transaction  has an  approximate  value between  $117.7  million and $134.9
million,  depending  on Business  Bancorp  shareholder  elections  and  assuming
UnionBanCal's  average  per share  price is  between  $32.00 and $55.00 for a 30
trading day period  prior to the  closing.  Under terms of the  agreement,  each
share of  Business  Bancorp  stock  will be  exchanged  - at each  shareholder's
election - either  for cash of $28.57 per share or for an amount of  UnionBanCal
Corporation  common stock  determined by an exchange ratio,  as follows:  if the
average closing price of UnionBanCal common stock is: (1) greater than $46.3275,
then the exchange ratio will be equal to $30.4271 divided by the average closing
price;  (2) equal to or between  $40.6725 and $46.3275,  then the exchange ratio
will equal 0.656782; (3) greater than or equal to $32.00 but


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less than $40.6725, then the exchange ratio will be equal to $26.7130 divided by
the average closing price; or (4) less than $32.00, then the exchange ratio will
be equal to 0.834781.  If the average closing price of UnionBanCal  common stock
is less  than  $32.00  or more  than  $55.00,  Business  Bancorp  may  choose to
terminate the agreement,  in which case,  UnionBanCal  has the right to complete
the  acquisition  by further  adjusting  the exchange  ratio as set forth in the
merger  agreement.  Shareholders will have the ability to state a preference for
receiving  cash,  stock,  or a mix of cash and stock in the  merger,  subject to
election and allocation procedures set forth in the merger agreement. Contingent
upon shareholder elections, between 45% and 100% of the total consideration paid
in the transaction will consist of UnionBanCal common stock. It is expected that
Business  Bancorp  shareholders  that  receive  UnionBanCal  common stock in the
merger will receive those shares in a tax-deferred  exchange. The transaction is
expected to be accretive to GAAP earnings per share in 2005.

The transaction has been approved by the boards of directors of Business Bank of
California,  Business Bancorp,  Union Bank of California,  N.A., and UnionBanCal
Corporation,  and,  subject to  regulatory  approval  and adoption of the merger
agreement by the shareholders of Business  Bancorp,  is expected to be completed
during the first quarter of 2004.

Based in San Francisco,  UnionBanCal  Corporation is a bank holding company with
assets of $42.7 billion at June 30, 2003. Its primary subsidiary,  Union Bank of
California,  N.A.,  currently has 277 banking  offices in California,  4 banking
offices in Oregon and Washington,  and 20 international facilities. The web site
is located at WWW.UBOC.COM.
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                                     # # #

This  communication is not a solicitation of a proxy from any security holder of
Business Bancorp. Business Bancorp, and its directors and executive officers and
other members of its management and employees,  may be deemed to be participants
in the  solicitation  of proxies from the  stockholders  of Business  Bancorp in
connection  with the  merger.  Information  about the  directors  and  executive
officers of Business  Bancorp and their  ownership in Business  Bancorp stock is
set forth in the proxy  statement for Business  Bancorp's 2003 annual meeting of
stockholders.  Employment  and  compensation  agreements  of  certain  potential
participants,  including  salary  continuation  agreements and change of control
agreements, are filed as exhibits to the Business Bancorp Form 10-K for the year
ended  December  31,  2002 and Form 10-Q for the  quarter  ended June 30,  2003.
Investors  may obtain  additional  information  regarding  the  interests of the
participants  by  reading  the  proxy   statement/prospectus   when  it  becomes
available.


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Shareholders of Business Bancorp and other investors are urged to read the proxy
statement/prospectus that will be included in the registration statement on Form
S-4, which UnionBanCal and Business Bancorp will file with the SEC in connection
with the proposed  merger because it will contain  important  information  about
UnionBanCal,  Union  Bank of  California,  Business  Bancorp,  Business  Bank of
California,  the merger,  the persons soliciting proxies in the merger and their
interests in the merger and related matters. After it is filed with the SEC, the
proxy  statement/prospectus will be available for free, both on the SEC web site
(HTTP://WWW.SEC.GOV) and from each of Union Bank of California and Business Bank
 ------------------
of California, by contacting:

John A. Rice, Jr., SVP - UnionBanCal Corporation Investor Relations,
                         (415) 765-2969
Alan J. Lane, CEO - Business Bancorp, (909) 888-2265

FORWARD-LOOKING STATEMENTS
- --------------------------
The  following  appears in  accordance  with the Private  Securities  Litigation
Reform Act: This press release includes forward-looking  statements that involve
risks and uncertainties. Forward-looking statements can be identified by looking
at the fact that they do not relate  strictly to  historical  or current  facts.
Often,  they  include the words  "believe,"  "expect,"  "anticipate,"  "intend,"
"plan,"  "estimate,"  "project,"  or words of  similar  meaning,  or  future  or
conditional  verbs such as "will," "would,"  "should,"  "could," or "may." These
forward looking statements include, but are not limited to, statements regarding
the  expected  benefits of the  transaction,  the  likelihood  and timing of the
closing  of the  transaction  and the  impact  of the  transaction  on 2005 GAAP
earnings per share. A number of important  factors could cause actual results to
differ materially from those in the  forward-looking  statements.  Those factors
include when and if the transaction is consummated, the success of Union Bank of
California in  integrating  Business Bank of California  into its  organization,
fluctuations in interest rates,  government policies and regulations  (including
monetary and fiscal policies),  legislation, economic conditions, credit quality
of borrowers,  operational  factors,  competition in the geographic and business
areas in which the Company  conducts its  operations,  and global  political and
general economic conditions.  Complete  descriptions of UnionBanCal  Corporation
and Business  Bancorp,  including  related risk  factors,  are included in their
public filings with the Securities and Exchange Commission,  which are available
online at  http://www.sec.gov.  All forward-looking  statements included in this
press release are based on information available at the time of the release, and
neither  UnionBanCal  Corporation nor Business Bancorp assumes any obligation to
update any forward-looking statement.






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