Here at the elegant Grosvenor House Hotel, at what is the oldest antiques fair worldwide, London dealers like Stair & Co. and Mallett say Americans account for 50 percent of their sales. Last year, a staggering $50 million was spent. Yet Americans make up only 13 percent of the 22,000 who attend each year, says fair spokesperson Luke Irwin. The event has long attracted clutches of Whitneys, Rockefellers and Kennedys. "Originally, Americans bought entire rooms of 'brown furniture,'" recalls Henry Neville, of London's Mallet, a founding member of the fair, which began in 1934.

This year 86 dealers from the U.K., U.S., France, Germany, Hong Kong, the Netherlands, Portugal and Switzerland are showing their wares. In the past, the focus was largely on older fine art and antique furniture and ceramics, but this year there is an abundance of contemporary paintings, and a greater diversity of dealers. Even Surrey garden ornament dealer Sweerts de Landas is participating.

One reason for the broadening of taste is the age-old case of supply and demand. "With fewer great objects to chase and more money chasing them, the entire antiques field has expanded," says Michael Pick, a Stair & Co director. But even with a wider range of items, dealers say that many Americans are still going for the English country house look.

The ingredients of that elegantly eclectic style are now considerably more sophisticated than a few years ago. Continental details and Asian accents are emphasized. For instance, a bonnet-topped or scrolled pediment secretary is de rigueur. Mallett has a splendid Queen Anne style example. Made in Germany in 1740, the scrolled-pediment secretary is in a soft olive green with chinoiserie detailing in gilt, and dates from 1740. The $1.7 million price tag is a showstopper too. (One dollar is approximately 1.68 pound sterling now.)

For the continental touch, Harris Lindsay has an extremely rare pair of English serpentine commodes with elaborately gadrooned borders. The pair was made ca. 1740 and bears a heavy French influence. Not to mention, the commodes have the kind of impeccable provenance that makes Americans swoon. Originally in the collection of the Marquesses of Ripon, the pair was later owned by the American titan Walter P. Chrysler. "The cost is one million dollars," says dealer Jonathan Harris, who last year at Grosvenor House sold pieces to the Getty and the National Gallery of Scotland.

A pair of George III, Gainsborough chairs are also quintessential to the American take on the English country house. Stair & Co. has two splendid examples. "They are the classic, powerful Fifth Avenue decorating statement," says Pick. Gilt mirrors are another staple of the look. London dealer Ronald Phillips is touting five mirrors, all from the 18th century, ranging in price from $142,000 to $252,000.

Old Master paintings perfectly complement such fine furnishings, and the Grosvenor House fair boasts no less than nine Old Master dealers, many of which carry standard textbook artists like Hobbema, van Ruysdael and van Ostade. Johnny van Haeften has an elaborate still life of grapes, peaches and the proverbial peeled lemon by Laurens Craen for $462,000.

Just as the specialties on view have diversified, so too have the client profiles. The new mega-millionaire buyers are best exemplified by two Americans battling over a $150,000 rare Ming altar table at Grace Wu Bruce of London and Hong Kong. "One is a major donor to the Metropolitan Museum who has his own distinguished collection, while the other client has a house in Southampton, N.Y., which indicates a more mass appeal," says Ms. Bruce. Doesn't that say it all about the burgeoning collector base at Grosvenor House?