When the wow wears off

Tate Modern's Andy Warhol exhibition, which closed last week, was the gallery's most successful exhibition by far. Some 4,000 paying customers a day filed through the show, which attracted more than 220,000 visitors in its seven weeks. By my reckoning, in terms of contemporary art, only the headline-grabbing Young British Artists' Sensation, at the Royal Academy, has surpassed these figures in recent years.

The Warhol show achieved its success not by contention, but by smart partnerships and great timing. For two months we saw Warhols writ large upon all of London's main thoroughfares. This was a Channel 4 advertising campaign to support its three-part documentary on Warhol. The Tate doesn't have such resources to promote a show; the best it could manage were some modest posters on the Underground. The television series was timed to run at the opening of the show and, while it barely registered a flicker on the ratings, it gave a massive boost to the Tate.

Warhol's philosophy made him perfect for such media promotion. He understood very well notions of branding. His work showed us how the mass-produced image entered every aspect of our lives. For our generation, they were more important images than great art. Then he made the images into great art, by reproducing them - again and again.

I would like to think that we now realise how much we need Warhol and how, some 15 years after his death, we are beginning to understand his legacy. The show was a critical as well as a popular success. Many reviewers took it as a redefinition of Warhol; he had become a "serious artist".

Warhol died in 1987. For a long time afterwards, the art world didn't quite know what to make of him, particularly of his later work. Indeed, his sale prices went down in the first months after his death, as panic ensued over whether his technique had produced just a little too much " product" to sustain values. But in the week of the Tate's show opening, a wave of Warhol hit the showroom; at the London Gagosian Gallery, prices were up to £175,000 apiece for the late paintings that even a year or two ago would have languished in the stock room.

In a place as small as the art world, commercial success, critical acclaim and attendance figures are intimately bound together. The Tate thrived on that convergence.

What made the Warhol show uniquely successful was its focus and presentation. It was clearly laid out over an entire floor. It made Warhol look good, and Tate Modern never looked better.

The benefits of a show like this to a museum such as Tate Modern are obvious. It's not just about the punters who pay for the exhibition. It attracts visitors who don't bother to queue for the blockbuster, and instead wander through the Tate's own collections, or stop to browse among the mugs in the gift shop (where the real cash is made). And things are looking good, too, for the next show, Matisse Picasso, with advance bookings of 20,000 six weeks before it opens.

Director Nicholas Serota pulled off nothing short of a miracle when he managed to carve a museum of modern art out of a power station, disfeverused for decades, on the wrong side of the river. But there is more to sustaining the miracle than offering a hit show. The time has now come for the Tate to look to its permanent collection and its display. It hasn't got the money for a consistent acquisitions strategy, and it has to rely on the generosity of occasional benefactors.

There has never been a Government policy to develop a national contemporary collection. But Tate Modern is, first and foremost, a great national collection, and it must be able to work with the things it owns and knows best.

Tate Modern will be two years old next month and, after a staggering 5.2 million visitors in its first year, the second-year figures will probably settle at around a still substantial 3.5 million.

For that, thank Andy. But take away the Warhol wow, and there are signs that the novelty is beginning to wear off. It is up to the curators now to deliver the goods in their programming to sustain these record levels of interest. The Warhol exhibition gives cause for optimism, but it must not be the show we look back on as the end of the beginning of Tate Modern.