Cornerstone Properties Announces Distribution; Declares $0.03 Per Share Special Distribution.

Business Editors

NEW YORK--(BUSINESS WIRE)--May 25, 2000

Cornerstone Properties Inc. (NYSE:CPP) announced today that the Company's Board of Directors has declared a special distribution in the amount of $0.03 per share. The distribution will be payable on June 15, 2000 to stockholders of record as of June 1, 2000.

This dividend was declared in order to satisfy Cornerstone's FIRPTA (Foreign Investment in Real Property Tax Act) withholding obligations under Section 1445 of the Internal Revenue Code with respect to net capital gain deemed paid to its non-U.S. stockholders since January 1, 2000. Cornerstone is withholding the entire amount of the special dividend with respect to each share of its common stock that is beneficially owned by a non-U.S. person on the record date. By withholding such amounts from the special dividend, Cornerstone will have withheld at the applicable 35% rate on the estimated deemed distributions of its net capital gain to non-U.S. stockholders for its short taxable year ending on the merger effective date.

Shareholders are urged to consult with their own tax advisor to determine the effect of the dividend on their individual tax situation, including any state, local or non-U.S. tax consequences.

Cornerstone Properties is a fully-integrated real estate investment trust (REIT) with a full range of development, acquisition, management and leasing capabilities. On February 11, 2000, Cornerstone announced that it entered into an agreement and plan of merger with Equity Office Properties Trust (NYSE:EOP). (See joint proxy statement/prospectus at www.cstoneprop.com). The Company currently owns 82 Class A office properties throughout the U.S. totaling over 17 million square feet and has an additional $687 million of projects under development. The properties are located in the major suburban markets and central business districts of Seattle, Northern and Southern California, Minneapolis, Chicago, Boston, New York, Washington, D.C. and Atlanta. For more information visit the Cornerstone Properties website at http://www.cstoneprop.com/. To sign up for our press release e-mail list, go to http://www.cstoneprop.com/e-mail.

This press release contains forward-looking statements within the meaning of the Federal securities laws. The forward-looking statements herein include statements about the proposed merger with Equity Office Properties Trust. Forward-looking statements are inherently subject to risks and uncertainties, many of which cannot be predicted with accuracy, that could cause the actual results, performance or achievements of Cornerstone to differ materially from those reflected in such forward-looking statements. The following factors, among others, could cause actual results to differ materially from those described herein: failure of the stockholders of Cornerstone or Equity Office to approve the merger, delays in consummating the merger and the inability to obtain, or meet conditions imposed for, governmental approvals of the merger. Information contained in this press release regarding current and future market conditions is based on Cornerstone's assessment of real estate markets as of this date and is subject to the uncertainties inherent in such an assessment. In particular, but not exclusively, national and regional economic conditions, the rate of new construction, and demand and supply in a given market will affect leasing activity, projected rents and the cost of lease renewals. Please see our periodic SEC reports, including our SEC 10-Q and 10-K filings, for a description of certain of these risks and uncertainties. Cornerstone is not under any obligation to (and expressly disclaims any such obligation to) update or alter its forward-looking statements whether as a result of new information, future events or otherwise.

Investors should read the joint proxy statement/prospectus regarding the proposed merger with Equity Office Properties Trust which became available May 17, 2000 because it contains important information. Investors may obtain a free copy of the joint proxy statement/prospectus from the SEC website at www.sec.gov. The joint proxy statement/prospectus may also be obtained for free by directing a request to Cornerstone Properties Inc., Tower 56, 126 East 56th Street, New York, NY 10022, Attn: Corporate Secretary, telephone: [phone].

The identity of persons who, under SEC rules, may be considered "participants in the solicitation" in connection with the proposed merger, and a description of their ownership interests in Cornerstone, is available in a filing on Schedule 14A made by Cornerstone on February 18, 2000, and available on the SEC website or at the address above.