Doping: Seán Kennytalks to the International Cycling Union president, Pat McQuaid, who knows, after all the doping revelations, this year's Tour de France is of vital importance to the sport's image.

There is a kind of poignancy to the moment. You have been asking Pat McQuaid about doping in cycling for perhaps half an hour when he breaks off the subject. The TV is on in McQuaid's office as he speaks, showing the Dauphiné Libéré, a major pre-Tour de France race.

"In the last 10 minutes I've seen Valverde, a pre-race favourite, go out the back. They're on the final climb up the Mont Ventoux at the moment and only a couple of minutes ago Vinokourov went out the back.

"He's the race leader; he won the stage yesterday and now he's dropped to the back, because he's human. They have good days and bad days."

The irony is doping seeks to smooth out such vicissitudes of human endurance. Blood-boosting EPO transfusions are meant to make every day a good day for the bent cyclist. Cycling has never had such consistently bad press as it has in the months leading up to today's Tour de France, with the possible exception of the Festina affair of 1998. Ivan Basso's admission in early May that he was involved in the Operation Puerto blood doping scandal has earned him a two-year ban.

On May 18th, the Floyd Landis farrago took on the lurid tones of soap opera. The doping tribunal investigating Landis heard that Greg LeMond, a witness, had been intimidated by Landis's (now former) manager Will Geoghegan in an attempt to prevent him testifying. LeMond was sexually abused as a child; Geoghegan knew this and threatened to make it public knowledge, contrary to the former's wishes.

Then on May 25th, Bjarne Riis, winner of Le Tour in 1996, admitted to having used illegal, performance-enhancing substances during that race and at other times during his career. Another day, another doping story.

The revelations came like bullets, further wounding the sport's already moribund credibility. Dubliner McQuaid, president of the International Cycling Union (UCI), has felt the sting more than most.

"Everybody - at the top end of the sport in particular - realises, after Operation Puerto and Floyd Landis, that we can't have any more of these scandals. Otherwise the sport won't survive. Everybody realises we have to work everyone towards a clean sport."

There are glass-half-full and glass-half-empty scenarios. McQuaid has taken an optimistic line in his public pronouncements. The argument goes that cheats are being exposed and that the process, though painful, will go towards healing the deep wounds doping has inflicted on the sport.

Another altogether darker view, expressed by many analysts of the sport, is that Basso, Landis and Riis are the visible tip of a mountain of corruption, otherwise wreathed in a fog of secrecy. The deafening silence of the peloton is a well-documented phenomenon. Can McQuaid affect change to such a deep-rooted culture?

"I think there's a stronger culture of anti-doping now and there's a greater likelihood riders will talk, and they are (riders have given evidence, having been issued with subpoenas, in the Operation Puerto case). You can only change a culture of silence when everybody is convinced we can't have any doping in the peloton. Day by day and bit by bit, that's the point we're approaching."

Doping circumscribed last year's Tour like police tape. The suspension of four top riders before the race was followed by Landis, its winner, testing positive for excessive levels of testosterone. The media trained its unrelenting glare on the sport. Cycling was news. Bad news.

"The Landis story was very, very damaging. That being on the front page of newspapers has a huge effect on the development of the sport because federations depend on governments, sports councils and Olympic committees for funding. It affects credibility and that affects the thinking of people who are making decisions about funding."

McQuaid knows this year's Tour is consequently of vital importance to the sport's image. "We need a clean Tour; the sport deserves a period of time now to try to regain its credibility without having any more scandals hit. They do take time to get over and they do damage the sport. I sincerely hope it's going to be a good Tour de France and we don't have any doping scandals."

Hope or expectation? "I think it will be clean because I know what's going on in the professional peloton at the moment. I know all the work the teams are doing (to counter doping)."

Whilst self-regulation by teams is something of an oxymoron, the UCI itself has instituted rigorous new anti-doping procedures. The "100 per cent against doping" programme includes random blood and urine testing without warning during training and rest periods, as well as tests prior to the major tours. The establishment of blood and DNA profiles of all riders on the pro tour is another element of the new regime. So far, 585 of the 600 pro tour riders have given their written consent to be DNA tested. Ominously, lawyers representing the other 15 have become involved.

"From the blood test results, we target certain riders. The ones who are the favourites coming up to the big tours, they would be targeted for increased out-of-competition controls leading up to the tours, because that's where they say any doping that's going on is done."

An anti-doping charter launched by McQuaid on June 19th aims to secure all pro tour riders' signatures by today, the day the Tour de France commences. The document seeks pledges that cyclists will provide DNA samples to the Spanish authorities investigating Operation Puerto and will pay a fine of one year's salary if caught doping in the future. Compliance is not legally enforceable, although McQuaid says a full list of those who have signed will be published on the UCI website.

He knows the Operation Puerto case looms darkly over cycling's future. "It (exposing the scandal) was a success for cycling but it's done a huge amount of damage because there's a lot of speculation as to who's in it and who isn't. There are lots of others apart from Basso who are being speculated on. It's hanging over the sport like the sword of Damocles until we finally get through the judicial process."

Alongside the mountain stages and the sprint finishes, there is the parallel race between those who enable doping and those who attempt to counter it. The sport's future may depend less on the races played out on the hot gritty roads and more on those silently contested in cool, pristine laboratories. The authorities, of course, are playing catch-up.

Previous tensions between the World Anti-Doping Agency (WADA) and the UCI have eased somewhat under McQuaid's watch, although with a rhetorical flourish, he describes WADA chairman Dick Pound as "a guy who speaks before his brain engages".

"We have an excellent relationship with WADA on a working level. There's no other sport that does as much as we do with regard to anti-doping. Even athletics, for instance; they won't do blood tests on the day of competition. They have to be done on the day before and they even tell the athletes they're coming. We do surprise blood tests on the morning of competition."

Cycling's image problem persists despite these efforts and yet the sport retains huge popularity, particularly in France and Italy. McQuaid wants coverage of this year's Tour to remain confined to the sports pages. "My best-case scenario would be good racing every day, that riders could be one day going well, the next day blow up . . . That people watching will think they're watching a proper, clean sporting event. We want it to be about excitement, drama and sport."

Sport. That is what it is supposed to be about. Meanwhile, the Landis doping tribunal in California will deliver its judgment some time soon. If Landis wins, the UCI will appeal to the Court of Arbitration for Sport.

Back on the road, all eyes are on this year's Tour de France.