The American Lung Association and the American Thoracic Society announced yesterday that they were moving their national headquarters from Midtown Manhattan to 61 Broadway, near Wall Street about four blocks from ground zero.

The 38,000 square feet of space the two nonprofit organizations will occupy is a tiny fraction of the 15.4 million square feet of downtown office space that sits vacant, according to TenantWise.com, a real estate company. But news that any commercial tenant was moving to a section of the city still reeling from the attack on the World Trade Center and corporate defections was cause for celebration by city and state officials and landlords.

Especially welcome was the news that the Lung Association was moving to a place where many New Yorkers are still concerned about the quality of the air. "It's a terrific sign of the potential and the health of Lower Manhattan that uptown companies and organizations are beginning to move downtown," said Carl Weisbrod, president of the Alliance for Downtown New York, a business group.

John L. Kirkwood, the president and chief executive of the Lung Association, said he expected to begin moving 80 employees to the new offices at the end of June, from the association's current space at 1740 Broadway, at 56th Street. The Thoracic Society, which also is at 1740 Broadway, expects its staff of 54 to move a couple of months later.

"We have done our due diligence and are comfortable with the indoor air quality of our new office space," Mr. Kirkwood said. "The offices have been thoroughly cleaned and tested, and we have concluded that there is no contamination."

There were widespread health concerns last fall about the presence of toxic substances like asbestos downtown. Mr. Kirkwood said the air quality had returned to pre-Sept. 11 levels, though that is far from perfect.

The Lung Association recently completed its annual report on air quality in more than 600 counties across the country. Mr. Kirkwood said New York, like nearly half the counties, got a failing grade.

"There is still a need for substantial improvement," he said. "This can be accomplished by reducing diesel pollution, lowering emissions from industrial facilities and strict enforcement of the federal Clean Air Act."

Mr. Kirkwood said the Lung Association and the Thoracic Society had been looking for a new home for some time with their brokers, Cushman & Wakefield. The groups will be subleasing space from Multex.com, an information and technology firm.

Mr. Kirkwood said he expected to save about 20 percent, or $250,000 a year, on occupancy costs. That does not count cash grants and tax breaks from the state and the city for companies staying or moving downtown.

Few employers have moved downtown from Midtown. On the other hand, Lehman Brothers and Aon, an insurance company, have announced moves to Midtown.