<PAGE>

                                                                    EXHIBIT 99.1


           M A C K - C A L I   R E A L T Y   C O R P O R A T I O N

     For Immediate Release

     Contact:  Mitchell E. Hersh             Robert Siegfried/Roanne Kulakoff
               Chief Executive Officer       Kekst and Company
               (908) 272-8000                (212) 521-4800


              MACK-CALI AND PRENTISS PROPERTIES TERMINATE MERGER


     CRANFORD, NJ and DALLAS, TX, September 22, 2000 - Mack-Cali Realty
     Corporation (NYSE: CLI) and Prentiss Properties Trust (NYSE: PP) announced
     the termination of their agreement to merge the two companies.

     Under the terms of the negotiated termination agreement, Prentiss
     Properties will acquire Mack-Cali's 270,000 square foot Cielo Center in
     Austin, Texas for $47.1 million. In connection with the transaction,
     Mack-Cali deposited $25 million into an escrow account for the benefit of
     Prentiss Properties.

     "While we still believe in the merits of the merger, the termination of the
     agreement at this point is in the best interests of both companies," said
     Thomas August, Chief Executive Officer of Prentiss Properties. "We're
     disappointed that the merger will not occur," said Mitchell Hersh, Chief
     Executive Officer of Mack-Cali. "This settlement however allows Mack-Cali
     and Prentiss to refocus on their core strategies."

     Mack-Cali Realty Corporation is a fully-integrated, self-administered,
     self-managed real estate investment trust (REIT) providing management,
     leasing, development, construction and other tenant-related services for
     its class A real estate portfolio. Mack-Cali owns or has interests in 266
     properties, primarily office and office/flex buildings, totaling
     approximately 28.2 million square feet, located in 12 states and the
     District of Columbia. The properties, which are primarily located in the
     Northeast, enable the Company to provide a full complement of real estate
     opportunities to its diverse base of over 2,400 tenants.

     Additional information on Mack-Cali Realty Corporation is available on the
     Company's Web site at www.mack-cali.com.

     Certain information discussed in this press release may constitute
     forward-looking statements within the meaning of the Federal Securities
     law. Although the Company believes that the expectations reflected in such

<PAGE>


     forward-looking statements are based upon reasonable assumptions, it can
     give no assurance that its expectations will be achieved. Forward-looking
     information is subject to certain risks, trends and uncertainties that
     could cause actual results to differ materially from those projected. Among
     those risks, trends and uncertainties are the general economic climate; the
     supply of and demand for office, office/flex and industrial/warehouse
     properties; interest rate levels; the availability of financing; and other
     risks associated with the development and acquisition of properties,
     including risks that the development may not be completed on schedule, that
     the tenants will not take occupancy or pay rent, or that development or
     operating costs may be greater than anticipated. For further information on
     factors which could impact the Company and the statements contained herein,
     reference should be made to the Company's filings with the Securities and
     Exchange Commission including quarterly reports on Form 10-Q, reports on
     Form 8-K, and annual reports on Form 10-K.






     #  #  #


<PAGE>


          M A C K - C A L I   R E A L T Y   C O R P O R A T I O N

For Immediate Release
Contact:  Mitchell E. Hersh             Robert Siegfried/Roanne Kulakoff
          Chief Executive Officer       Kekst and Company
          (908) 272-8000                (212) 521-4800


          MACK-CALI REALTY CORPORATION AND PRENTISS PROPERTIES TRUST
                     TERMINATE MERGER AGREEMENT

-  Mack-Cali to Focus on High-Barrier-to-Entry Markets, with Particular
   Emphasis on Mid Atlantic and Northeast Corridor, to Build Shareholder
   Value -

        MACK-CALI ANNOUNCES ENHANCED COMMON STOCK REPURCHASE PROGRAM

CRANFORD, N.J.- September 22, 2000- Mack-Cali Realty Corporation (NYSE: CLI)
announced today that Mack-Cali and Prentiss Properties Trust (NYSE: PP) have
mutually agreed to terminate their previously announced merger agreement. In
addition, Mack-Cali's Board of Directors has authorized an increased share
repurchase program through which Mack-Cali is authorized to repurchase up to
$150 million of its outstanding common stock in the open market or through
private transactions with the amount and timing of repurchases depending on
market conditions. The Board previously had authorized the repurchase of up to
$100 million of Mack-Cali common stock, of which the Company has already
purchased approximately $52.6 million. Mack-Cali currently has 73.3 million
shares and units outstanding.

Mitchell E. Hersh, chief executive officer of Mack-Cali, stated, "The
priority of the Board of Directors and management of Mack-Cali is to achieve
enhanced shareholder value. We have carefully explored where Mack-Cali is
today and concluded that having the flexibility and authorization to
repurchase up to $150 million Mack-Cali common shares is a prudent use of our
resources given our confidence in the long-term potential of the company."

According to Mr. Hersh, the Mack-Cali Board determined that termination of the
merger agreement with Prentiss Properties also is in the best interests of
Mack-Cali shareholders after lengthy discussions with Prentiss Properties and an
extensive internal strategic review conducted to identify Mack-Cali's strongest
growth prospects. Mack-Cali worked with Donaldson, Lufkin & Jenrette in
connection with the strategic review and with Prudential Securities Incorporated
and Donaldson, Lufkin & Jenrette with respect to the Prentiss transaction.

"We have determined that it is in the best interests of Mack-Cali and its
shareholders that we implement a highly focused growth strategy geared to
attractive opportunities in high-barrier-to-entry markets, including locations
such as California, but primarily predicated on our strong presence in the
Mid-Atlantic and Northeast regions and an experienced operating infrastructure
to take advantage of attractive opportunities consistent with this growth
strategy."

Mr. Hersh concluded, "By pursuing this strategy, the Board and management team
of Mack-Cali fully expect to realize greater operating efficiencies,

<PAGE>

enhanced net asset values and increased financial flexibility, and, in turn, to
build greater value for shareholders in the form of strengthened financial
performance, a higher dividend and a larger share repurchase program."

Under the terms of the negotiated termination agreement, Prentiss Properties
will purchase from Mack-Cali for $47,175,000 Mack-Cali's 270,000 square-foot
Cielo Center in Austin, Texas. The property was acquired by Mack-Cali in
March 1998 for $37.4 million. In connection with the termination, Mack-Cali
also deposited $25 million in an escrow account for the benefit of Prentiss
Properties. This transaction is consistent with Mack-Cali's ongoing focus on
the Mid Atlantic and Northeast regions and will be among other strategic
property divestitures to further enhance Mack-Cali's financial strength.

Mack-Cali Realty Corporation is a fully-integrated, self-administered,
self-managed real estate investment trust (REIT) providing management,
leasing, development, construction and other tenant-related services for its
class A real estate portfolio. Mack-Cali owns or has interests in 266
properties, primarily office and office/flex buildings, totaling
approximately 28.2 million square feet, located in 12 states and the District
of Columbia. The properties, which are primarily located in the Northeast,
enable the Company to provide a full complement of real estate opportunities
to its diverse base of over 2,400 tenants.

Additional information on Mack-Cali Realty Corporation is available on the
Company's Web site at www.mack-cali.com.

Certain information discussed in this press release may constitute
forward-looking statements within the meaning of the Federal Securities law.
Although the Company believes that the expectations reflected in such
forward-looking statements are based upon reasonable assumptions, it can give
no assurance that its expectations will be achieved. Many factors could cause
Mack-Cali to delay or modify its self-tender offer. Forward-looking
information is subject to certain risks, trends and uncertainties that could
cause actual results to differ materially from those projected or cause
Mack-Cali to delay or modify its self-tender offer. Among those risks, trends
and uncertainties are the general economic climate; the supply and demand for
office, office/flex and industrial/warehouse properties; interest rate
levels; the availability of financing; and other risks associated with the
development and acquisition of properties, including risks that the
development may not be completed on schedule, that the tenants will not take
occupancy or pay rent, or that development or operating costs may be greater
than anticipated. For further information on factors which could impact the
Company and the statements contained herein, reference should be made to the
Company's filings with the Securities and Exchange Commission including
quarterly reports on Form 10-Q, current reports on Form 8-K, and annual
reports on Form 10-K.