THE moment of truth has arrived for 15 Central Park West, the limestone-clad retreat for the rich and very rich.

Two penthouses there have quietly gone on the market in the last few weeks at astronomical prices (starting at $80 million), and according to brokers, they are already attracting interest from a stream of billionaires and their representatives.

If either apartment sells at anything close to the asking price of more than $15,000 a square foot (not counting terraces or separate space for staff), the sale will set a record for the most expensive Manhattan apartment and confirm the place of the 15 Central Park West complex, designed by Robert A. M. Stern, atop the firmament of New York residential real estate.

If they fail to sell (like the tower triplex apartment at the Pierre Hotel, which has been on the market for $70 million since the fall of 2005), one may conclude that a fair measure of hyperbole has been mixed in with the limestone, marble, quarter-sawn oak and Venetian plaster that grace the lobby and public spaces of 15 Central Park West.

One of the apartments — a duplex on the 18th and 19th floors of the 20-story building closest to Central Park at West 61st Street — is so exclusive that the brokers — Felise Gross, Janet Gifford and Diane Abrams of Brown Harris Stevens — were not allowed to formally list it, or even set a firm asking price.

The seller, Dr. Lindsay Rosenwald, senior managing director of Paramount Capital Asset Management in addition to being a medical doctor, has talked about selling the unit for $100 million or more, but brokers have been quietly told that he would entertain offers of at least $90 million.

The apartment has 5,870 square feet of space, with four bedrooms, including a sprawling master suite, a private elevator and more than 1,100 square feet of terraces, mostly facing Central Park.

The second penthouse on the 40th floor, near the top of the second tower, closer to Broadway, is 5,270 square feet. It has four bedrooms and includes a separate ground-level space of 1,100 square feet for a home office or for a personal assistant. The apartment went into contract in 2005 and closed in April for $21.9 million, and it is now on the market for $80 million.

Richard Wallgren, a broker who represented the developers, Arthur and William Lie Zeckendorf, in many of the original sales, said the owner, a European, was “not going to be spending as much time in New York as he used to and decided to put it on the market.” Mr. Wallgren, who is also affiliated with Brown Harris Stevens, said he was in the process of officially listing the apartment. “The market continues to be very brisk for this building; there is lots of interest,” he said.

The apartment was bought by a corporation in care of a private Geneva-based company, Lemuria Alliance S.A., which listed Amit Ben-Haim as its chairman. Mr. Ben-Haim, a London investor, earned a fortune in medical devices and other businesses, starting in 1999 with the sale of an Israel-based medical device company founded by his brother to Johnson & Johnson for $400 million.

Each apartment has distinctive features. The duplex has 11-foot ceilings and a terrace that looks directly down on the canopy of trees of Central Park. The 40th-floor apartment has 14-foot ceilings and aerial views of both the park and the Hudson River and beyond.

Sharon Baum, a broker for the Corcoran Group not involved in the listings, said that despite foreclosures and falling housing prices around the country, prices at the high end were still rising sharply. “There is a lot of money,” she said. “The value of an apartment is what somebody is willing to pay.”