And as one star or star group's clothes, first recordings, guitars, and even school books become expensive, collectors cast around for new heroes to spend their money on.But Stephen Maycock, Sotheby's specialist in rock 'n' roll memorabilia, believes this is still a very young and unstable market He says: "If you like something, fine. But I wouldn't buy it as an investment."Madonna's pointy bras, for example, have deflated since their peak A few years ago they sold for pounds 4,000. But the market became flooded with her underwear and Madonna herself has waned in popularity. As a result, the bras are now worth half the sum.Michael Jackson's fedora hats have suffered a similar fate. There are too many of them on the market, and Whacko Jacko has also lost a lot of his appeal.However, the death of a rock star does great things for the value of memorabilia. Sets of Queen autographs rose from pounds 60 to pounds 600 overnight when Freddie Mercury died. Sets of autographs from The Rolling Stones before Brian Jones died are sold at a premium, as is gear from Hendrix, Joplin and Jim Morrison.

Kurt Cobain, nihilist lead singer of Nirvana, is growing as a teen cult symbol. His autograph leapt in price, from pounds 40 to between pounds 250 and pounds 600 overnight, after his suicide.Peter Doggett, editor of Record Collector magazine, says it helps if your star had a pretty face, deep inner meanings, poetic leanings, and captured young people's imagination - like Cobain and Jim Morrison.He adds that less profound bands, such as Slade, do not tend to attract collectors in the same way, although their records continue to be played on the radio.Investing in up-and-coming bands is a far more speculative and risky venture, although the potential rewards are great. Che Osborne, assistant manager of Beanos, says Oasis is going to dominate the world this year. But Mr Owen wonders whether the band has the staying power to make it over the longer term.The Oasis collectors' market grows apace. The band's promo-only debut 12-inch single, Colombia, sold for pounds 10 in late 1994. Two years later, it is worth more than 10 times as much.Alanis Morrissette, Sheryl Crow, Blur and Manic Street Preachers have also been tipped. Smashing Pumpkins are coming up and so is techno-punk band The Prodigy, whose first single, What Evil Lurks, on XL Records, is currently worth pounds 60.

Mr Doggett believes it will sell for pounds 200 by the end of the year.Auctioneers are probably the best place to go to buy higher-ticket items of memorabilia, over pounds 200. The cut is lower than that of the dealers: Sotheby's charges 15 per cent on the seller as well as 15 per cent on the buyer. There is no guaranteed price, so prices may go higher here than at dealers, although a sale may also bomb. Dealers, on the other hand, generally charge a 100 per cent mark-up, or two-thirds on a higher- ticket item. Records usually sell through dealers, unless there is something especially rare about a piece of vinyl.Alternatively, to cut out the middleman, try classified ads in music papers like Record Collector or other specialist magazines.As with most collectables, you have to know what you are doing or you will waste your money. Mr Owen says would-be collectors should focus on an area they like, and learn all they can. You can build extra value to your collection by gathering an entire set of items around a particular theme - such as Sheryl Crow's outfit and guitar from the LiveAid concert at which she played with Bob Dylan.You should always buy items in perfect or near-perfect condition.