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                                                                    Exhibit 99.1

                                                         Contact: Meredith Leyva
                                                                  (202) 828-8821
                                                            leyvam@fleishman.com


COSTAR GROUP NAMES LAWRENCE J. DRESSEL AS CHIEF OPERATING OFFICER

FORMER COO OF INTEREALTY.COM TO OVERSEE COSTAR'S SALES, MARKETING, PRODUCT
DEVELOPMENT, OPERATIONS AND CUSTOMER SERVICE

BETHESDA, MD - September 26, 2000 - CoStar Group, Inc. (Nasdaq: CSGP), the
leading provider of Internet-based information services to the U.S. commercial
real estate industry, today announced that Lawrence J. Dressel has been named
Chief Operating Officer (COO).

Mr. Dressel is the former COO of Interealty.com, a leading provider of
information systems, services and software applications to residential Multiple
Listing Services (MLS) and more than 250,000 real estate professionals
throughout the United States and Canada. He will report to CoStar CEO Andrew
Florance and have responsibility for the day-to-day management of operations,
product development, sales, marketing, and customer service.

"Larry brings CoStar strong leadership in product innovation and unyielding
focus on customer service with a proven ability to produce results," said CoStar
CEO Andrew C. Florance. "His expertise in designing and selling complex
technical products, developing and marketing comprehensive real estate
management systems, and managing large scale operations makes him an outstanding
choice for CoStar's COO."

Mr. Dressel has extensive management experience, most recently transforming
Interealty into a profitable company by increasing customer satisfaction through
establishment of "best of class" management practices, greatly improving
employee morale while realizing substantial cost reductions, and overseeing the
rollout of six new systems and services. Mr. Dressel managed more than 400
individuals in marketing, sales, professional services, finance, publishing,
customer service, development, and network services. Before joining Interealty,
Mr. Dressel spent over 10 years at The Fairchild Corporation, a
telecommunications firm and maker of aerospace and other technologies, where he
served in a variety of roles with increasing managerial responsibility. As
Senior Vice President and General Manager of Fairchild Communications, Mr.
Dressel helped grow the telecommunications division from a start-up to a very
profitable company with over 700 employees in 25 offices and $180 million in
revenue. Dressel later played a key role in the $700 million sale of Shared
Technologies Fairchild.


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Throughout his career, he has displayed strategic expertise in domestic and
international business management, partnership development, strategic planning,
sales and manufacturing operations in rapid growth companies. A hands-on leader,
Mr. Dressel possesses a proven record of surpassing revenue and profit goals,
reducing costs, and improving customer service, as well as the ability to
acquire and integrate companies.

"My expertise will help CoStar deliver valued added products and services to its
customers, while enhancing the day-to-day management of a true technological
leader in the real estate industry," Dressel said. "Equally important, my
successful experience in operational management gives me the ability to help
CoStar achieve its goal of strong growth and profitability."

For a digital photo of Mr. Dressel, please contact Meredith Leyva at (202)
828-8821.

ABOUT COSTAR GROUP, INC.

Headquartered in Bethesda, MD, CoStar Group, Inc. is the leading provider of
information services to the U.S. commercial real estate industry. CoStar's suite
of products offers customers access to the most comprehensive, verified database
of U.S. commercial real estate information in over 50 markets. The Company has
over 1,000 employees and contractors nationally, including over 700 highly
trained commercial real estate research professionals in 27 offices.
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This news release includes "forward-looking statements," which involve many
risks and uncertainties that could cause actual results to differ materially
from these statements. Important factors that could cause actual results to
differ materially include, but are not limited to, those stated in CoStar's Form
10-K for the year ended December 31, 1999 and those stated in CoStar's Form S-3
filed June 16, 2000. In addition to these statements, there can be no assurance
that CoStar will continue to have strong growth or reach profitability.