Cornerstone Properties Divests Six Non-core Properties.

NEW YORK--(BUSINESS WIRE)--SEPT. 17, 1999--

Three Transactions Total $103,275,000; Exits Phoenix Market

Cornerstone Properties Inc. (NYSE:CPP) announced today that it has sold six small, non-core properties for a total of $103,275,000. The divested properties include its Phoenix portfolio, one property in Pleasanton, California and one property in Los Angeles County. The Phoenix properties -- Biltmore Lakes Corporate Center, One and Two Gateway Center and Scottsdale Centre - which total 585,648 square feet, were sold to Chicago-based CMD Realty Investors for an aggregate amount of $71.5 million. The 70,355 square foot Pleasanton property, Foothill Corporate Center, sold for $10 million to an undisclosed buyer and the 141,732 square foot Tri-Center Plaza, located in Van Nuys, California sold for $21,775,000 to Lowe Enterprises.

Matt Moran, Chief Investment Officer of Cornerstone Properties, commented, "Phoenix is a market where we believe it would be difficult to build the critical mass required to optimize our business management model. The Pleasanton and Van Nuys assets, while in strong sub-markets, do not fit the current Cornerstone investment criteria relative to size and quality. We are pleased to continue the trimming of our asset base and the recycling of capital into the six core markets which comprise the fastest-growing markets in our asset class - Seattle, Northern and Southern California, Boston, New York and Washington, D.C."

Cornerstone Properties Inc. is a self-administered equity real estate investment trust (REIT) investing in Class A office properties in prime locations in major suburban markets and central business districts. The Company, through its subsidiaries, currently owns interests in 89 Class A office properties throughout the United States totaling over 19 million square feet. Cornerstone's common stock is traded on the New York Stock Exchange under the ticker symbol CPP.

This press release contains forward-looking statements within the meaning of the Federal securities laws. 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. 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.

For more information on Cornerstone Properties visit Cornerstone Properties' Web site at http://www.cstoneprop.com