On most days, a white, crocheted bikini isn’t appropriate attire at the Morgan Library. But when Oscar de la Renta used the piazza of the renovated museum to show his resort wear collection, a model in just such an outfit strutted out unashamed. During that same week, bold-faced names like Lindsay Lohan, Alicia Keys, and Ralph Lauren flocked to the New York Public Library for the Council of Fashion Designers of America Awards. That evening, the library was filled not with threadbare students but glitterati in sparkling dresses.

New York is full of glamorous event spaces, restaurants, and hotels that function as party venues. But when a host wants a dash of sophistication, the hallowed halls of cultural spaces beckon. Most of New York’s greatest institutions — including the Metropolitan Museum of Art, the New York Public Library, the Museum of Modern Art, the Morgan Library, the Frick Collection, the Guggenheim, the Whitney, Lincoln Center, and the American Museum of Natural History — all lead a remunerative second life as venues for corporate and social events.

The artsy venues lend class and, in the case of a corporate function, a mantle of cultural responsibility.”It’s a bigger draw than something in the same old ballroom or hotel or restaurant, and it lends a certain cultural cachet or validation to whatever the event is,” the president of the Kreisberg Group, an arts-related public relations firm, Claire Whittaker, said.

Event planner David Monn, of David E. Monn, LLC, said one of his clients would choose a cultural venue because of “their belief in that organization — it being special to them from a personal point of view.” Mr. Monn, who planned a dinner in May for Morgan Library trustees to inaugurate the new building, said the Morgan has that kind of special meaning to Mr. and Mrs. de la Renta, the latter of whom is a trustee.”Oscar and Annette are very, very fond of it, and Oscar doing his fashion show there was really to show his passion for the new space,” he said.

Although occasionally museums will give discounts to other nonprofits, in most cases the costs for entertaining are quite high. Ms. Whittaker, for instance, organized several parties for the Rolex Mentor and Protégé Arts Initiative. The launch party, in 2002, for about 150 guests, was at the Frick. “We wanted a nice art place that was elegant, and hadn’t been done and redone and redone as a party venue,” Ms. Whittaker said.

In subsequent years, she organized two large galas for the Rolex program in the lobby of the New York State Theater, where City Opera and New York City Ballet perform. “Having launched it at the Frick, in a visual arts place, it seemed like it would be good to go to a performing arts place,” she said. “And Lincoln Center has a strong meaning to the world of the arts.”

Museums allow their spaces to be used as party sites despite the risks to their collections and the general wearand-tear on the facility for good reason. It’s a powerful generator of support, and parties bring new names through the door.

“Corporate events often bring in new constituencies who would not otherwise know about the museum,” the Met’s vice president for development, Nina Diefenbach, said. “They get the privilege of seeing the museum when it’s shut to the public, which might entice them back. In fact, we know that happens. Any kind of audience-building that we can do is very valuable.”

“It’s a form of viral marketing,” the CEO and founder of BizBash, an eventplanning trade magazine, David Adler, said. “The type-A personalities don’t go to museums during the day, but they’ll go for a party in the evening. They might say, ‘I want to have my event here,’ or,‘I’d like to be involved.'”

In most cases, the host must make a substantial donation for the opportunity to entertain. On top of that, there is a fee, usually several thousand dollars, to pay for added costs like security. By far the most expensive venue is the Met. The museum allows only corporate — not personal — events, and the firm must be a member at the level of $60,000 a year or above. The Met declined to specify the event fees for its various spaces, which include the Great Hall, the Temple of Dendur, and the American Wing. (In 2004, the publication party for President Clinton’s “My Life” was held in the Great Hall.)

Ms. Diefenbach downplayed the importance of entertaining privileges in the Met’s fund-raising drives, calling it “only a small part of our corporate membership structure, for the highest level of membership.” She continued: “If you look at the percentage of support we get from corporations, it’s not driven by their need to entertain, it’s driven by their philanthropic interest in supporting nonprofits, and ones that are of interest to their employees.”

At the Frick Museum, things are different. “It’s a huge part of fundraising,” the head of special events, Colleen Tierney, said. There, a donation of $35,000 is required, and expenses on top of that run between $10,000 and $15,000. If the advantage of the Met’s spaces is their stately grandeur, the draw at the Frick is its small scale and its past as a private mansion.

Unlike the Met, the Frick allows personal events like birthday parties and wedding receptions (but not the ceremonies). Other institutions that allow wedding receptions include the Museum of Natural History ($5,000 donation required) and the Public Library ($2,500 donation required).

Some bucolic spaces, like the Brooklyn Botanic Garden and Wave Hill, a 28-acre former estate and public garden in the Bronx, have made weddings their primary business. The Botanic Garden does not require a contribution; it gets a percentage of the fee paid to the caterer, the Palm House. Wave Hill requires a contribution of $5,000 and a fee of $1,000.

“The reason why we do it is for the income basically,” Wave Hill visitor relations manager, Earl Martin, said. “We have a lot of guidelines and rules to make sure our public function isn’t impeded and that nothing’s damaged.”

Private individuals get a tax advantage in paying for a personal event through a donation to a nonprofit (which is deductible), rather than a straight fee. Corporations, however, do not, but they can almost always deduct events as a business expense. According to Jeffrey S.Tenenbaum, an expert in nonprofit organization law, a company paying for an event by making a donation to a tax-exempt organization “can either take the cost as a business expense deduction, as marketing or advertising, or they can take a charitable deduction. And they might want to do that, because some corporations want to show that they spend more money on charitable donations.”

For tax-exempt organizations that provide the space, the tax implications are even more complex. Contributions are not taxed because they go directly to activities that constitute the institution’s tax-exempt purpose.Income that institutions take in as event fees, however, may qualify as “unrelated business income,” and be taxed. “Generally, unrelated business income is being earned from an activity that’s unrelated to their main purpose or mission,” explained Mr. Tenenbaum. In the fiscal year 2004, for example, the Met reported unrelated business income from corporate events of $665,877.

Is there any down-side to opening up the spaces to the private events? Things can get a little crazy, according to Wave Hill’s Mr. Martin. “Once in a while, there’s the overzealous wedding that tries to do something they shouldn’t — like try to drive a truck across the grass,” he said. “But usually we’re very hands-on.”