Billionaire Mt. Lebanon High School graduate Mark Cuban, rumored previously as a buyer of the Penguins and Pirates, made his first investment in Pittsburgh yesterday -- a nine-story Downtown building overlooking the Allegheny River and PNC Park.

The flamboyant owner of the pro basketball Dallas Mavericks is the primary investor in the vacant building at 632-642 Fort Duquesne Boulevard, last occupied by the Easter Seals of Western Pennsylvania.

Mr. Cuban's partners in the purchase, which closed yesterday, are Todd Reidbord and Gregg Perelman of Walnut Capital Partners, the fast-growing Shadyside real estate firm.

Mr. Cuban and Mr. Reidbord were school mates at Mt. Lebanon and remain close, attending baseball and college basketball games when the 47-year-old Mr. Cuban is back in town once or twice a year. Mr. Cuban's parents live in Mt. Lebanon.

There are no immediate plans for the 88-year-old, 162,000- square-foot building. But Mr. Reidbord said the partners were "leaning toward some sort of residential use."

The property, once a glass warehouse for PPG Industries, features unobstructed views of the river and the ballpark, and it sits between the Byham Theater and an 18-story apartment building still under construction at the corner of Fort Duquesne Boulevard and Seventh Street.

Asked about the real estate purchase in an e-mail, Mr. Cuban wrote: "I think Pittsburgh is a good investment" and declined further comment, referring all questions to Mr. Reidbord.

Mr. Reidbord said his high school friend received a package in the mail last fall advertising the sale of the building, at an asking price of $8 million. Mr. Cuban called Mr. Reidbord and said " 'we should look at the building.' "

"I know he is very bullish on Downtown," Mr. Reidbord said. "He just sees value there."

Mr. Reidbord declined to disclose the purchase price, other than to say that it was "less" than $8 million. The seller, local developer Joe DeMartino, bought it in 2004 for $5.2 million with plans for a luxury hotel.

Born in Squirrel Hill, Mr. Cuban got his start as an entrepreneur by selling garbage bags in the South Hills.

Ever since making his fortune by selling Internet company broadcast.com to Yahoo in 1999 and then purchasing the Mavericks in 2000, Mr. Cuban has been mentioned as a possible investor in the Penguins and the Pirates.

Last summer, after he expressed an interest in the Pirates if the team ever came up for sale, fans decorated the stands at PNC Park with pleas for Mr. Cuban's involvement. "Mr. Cuban, Please Buy Our Bucs" read one white-cardboard sign on a night when Mr. Cuban was in the stands.

Could the Downtown real estate purchase be the first of many investments in Pittsburgh for the outspoken entrepreneur? The Penguins, after all, officially are for sale, according to team owner Mario Lemieux. Mr. Cuban, former host of a short-lived TV reality show called "The Benefactor," declined to respond yesterday to such questions.

In the meantime, Mr. Cuban is in "no hurry" to redevelop the Fort Duquesne Boulevard building, Mr. Reidbord said. Instead, he is leaving that job to his high school buddy and his partner, Mr. Perelman, who together own several high-profile buildings on Shadyside's Walnut Street and in the Strip District.

"Mark has said to us, basically, he has a long-term horizon," added Mr. Reidbord. He wants the two local real estate executives to figure out " 'what the best thing to do with the building is.' "