Why is the normally decorous Bonham's being taken over by a host of brassy dames in scanty clothing?
It is 10 years since Bonhams launched sales of erotica and five years since it abandoned them. Would-be vendors inundated the auctioneers with boring reproduction Oriental soft-porn prints and ivories. It was difficult to find original, tasteful erotica.

Now Bonhams is launching Nudes in Art picture auctions. The first, on Thursday, starts at 6pm in order to tempt after-work private buyers. Most picture dealers think it will flop: after all, who collects only nudes? But it is a new theme, and one that could appeal to those who have never bought art before - besides the merely lascivious.

That is the trouble with selling sexy art. Those prepared to bid for quality - over pounds 100,000, say, for a life-size Poynter or Alma-Tadema of an undraped slave girl in classical pose - prefer to attend major auctions of Victorian pictures, not sex-theme sales full of artless voyeurs with modest incomes.

Estimates at Bonhams' nudes sale are comparatively low: from pounds 100 to pounds 22,000. There are no Poynters or Alma-Tademas, not even a Picasso - although about a third of the Picassos in the big auctions are erotic. Does the economic ratchet of erotica inevitably drive down taste as it drives down price?

There are certainly some pretty brassy Continental dames among the 111 lots. The Reclining Female Nude by the Hungarian Pal Fried (d.1955) is not so much reclining as actively soliciting (est pounds 1,500-2,000). And the reclining nude by the Frenchman Henri Montassier (d. 1946, est pounds 6,000- pounds 8,000) gives new meaning to the auctioneers' tag "The Property of a Gentleman".

For those who disdain blatant attempts to arouse, there are Victorian life-class drawings of the kind in such profusion last year in the sales of Rudolf Nureyev's estate. Here is a seated, contemplative old man with pot belly and Noah's beard, drawn in pencil by Herbert Wilson Foster, the Stoke on Trent figure painter, in 1884 (before fine draftsmanship and pencil, charcoal and pastel had become unfashionable). The estimate is pounds 100-pounds 150. A studio study of nudes in pencil by the better-known Sir William Orpen (d.1931), is est pounds 300-pounds 500.

The nouveau art posters and prints by the Frenchman Alphonse Mucha (d.1939) are zooming up in price after being dropped by the money-troubled Japanese five years ago. In Christie's South Kensington's poster sale, Thursday (10.30am), the estimate on Mucha's Salon Des Cents poster of 1896, with classic image of a bare-breasted woman with headband, is pounds 7,000-pounds 9,000 - not far short of the pounds 10,000 it might have fetched during the boom. Since then, prices have been down by a half or more.

Latest downer: Twenties posters by the Frenchman Adolph Cassandre. His highly stylised "Wagons Lits Cook", est pounds 3,000-pounds 5,000, might have fetched pounds 4,000-pounds 6,000 a year ago. The trouble is that the Twenties are no longer the only period favoured by "retro" enthusiasts. Today, the Sixties are big. Even the Eighties has devotees. He'll be back.