Insuring the priceless: a new documentary film shows the world's art treasures are at great risk.

Works of art may be priceless, but not to thieves. And the vulnerability of such treasures may be greater than the average person thinks.

Filmmaker Rebecca Dreyfus reports the value of the most expensive art heist in the United States at $500 million. That occurred in March 1990 at the Isabella Stewart Gardner Museum in Boston, where two thieves took 13 paintings, including Rembrandt's Christ in the Storm on the Sea of Galilee and Vermeer's The Concert. The thieves were dressed as police officers, were let inside by guards, and reportedly spent about two hours methodically removing the paintings they wanted.

"The most shocking thing was that it was done with such planning," said Dorit Straus, worldwide fine-art manager for the Chubb Group of Insurance Cos. "It was like a movie. Thieves dressed up as cops, and guards opened the doors for them."

Also of interest: The museum did not insure the paintings. Strans said many museums don't buy such insurance for various reasons. Sometimes it's how trusts are set up, she said. Many institutions simply can't afford to buy insurance. Others may be state-owned, and the states choose to self-insure .Whatever the case, she rejects the notion that no amount of money could replace art work that is lost. "Even if they can't purchase the same thing, they would get working capital to replace the collection" she said. "Then, there's the matter of the fiduciary responsibility institutions have to board members and the public to educate. At the end of the day, there's a price for everything."

Unfortunately, nothing has as yet been recovered from the Gardner heist, though Straus said she retains optimism that the paintings have not been damaged or destroyed and that they will someday be recovered. Sometimes it takes 20 to 25 years for stolen art to be found, she said.

Dreyfus was so upset at the lack of progress in the Gardner case that in 2002, she decided to make a documentary film exploring The Concert and its theft. Described as stirring and visually stunning, the film re-started efforts by law enforcement to solve the case. This was due in large part to private art investigator Harold Smith, whom Dreyfus had contacted for information but who became part of the film when he renewed his search for the Gardner art. Along the way, he initiated a publicity blitz with publications, set up a 24-hour hotline, and traveled at length in the United States and Europe. The film, Stolen, became part of Smith's legacy; he died in February 2005, shortly after the film was finished.

The stakes have never been higher in protecting the world's art treasures. Straus said the value of single paintings has eclipsed the $100-million level. And valuable art is even more vulnerable in places other than museums, such as churches, private residences and archeological sites, especially in countries without first-world economies. Transport also is dangerous. In November, F.B.I. officials recovered a Goya painting after thieves had stolen it from a truck parked overnight at a Howard Johnson Inn in Pennsylvania.