Scores of athletes converging on Vancouver may be experiencing a peculiar Olympic welcome.

Many are being asked to roll up their sleeves, pull down their trousers or both. Despite the way that sounds, it's not some perverse hazing ritual. It's doping control.

In the days leading up to the start of the quadrennial celebration of winter sport, lots of athletes are receiving word the World Anti-Doping Agency or their national Olympic committee or their international sports federation want to test them for banned substances.

Some competitors may end up being tapped for samples more than once. And athletes participating in sports in which doping is known or suspected to be a problem may find themselves particularly targeted. Think cross-country skiing and biathlon. Curlers, on the other hand, may draw fewer short straws.

It is because the folks trying to foil the cheaters know those who dope may plan to slip in a last-minute course of steroids or red blood cell generating erythropoetin (EPO). The anti-doping forces will be trying their darnedest to keep dirty athletes from competing with clean ones.

Some veterans of the fight think progress has been made.

"I'd say the white hats are gaining,'' says Dick Pound, a longtime and influential member of the International Olympic Committee.

Pound, a Montreal lawyer, was the founding chairman of the World Anti-Doping Agency and still sits on WADA's board.

"I mean, I think the interval between let's say the commencement of the use of a substance or method and our ability to detect it has shrunk considerably. And you're forcing people into more and more sophisticated areas of medicine, which lend themselves to more and more sophisticated detection and so forth.''

"But it's not the Wild West the way it used to be,'' he says.

Still, the period just before the Games is a particularly critical juncture in the ongoing tussle between athletes who dope and those trying to root out this kind of behaviour.

"We have learned, for example, that there are windows very close to competition but not during the competition itself, where an athlete will micro-dose with EPO for example,'' explains Paul Melia, president and CEO of the Canadian Centre for Ethics in Sport, which conducts Canada's anti-doping program.

"The synthetic EPO drug will have cleared the athlete's system by the time of competition, but the benefits will still be there. So a lot of testing is done just before the Games take place.''

The goal is to try to avert situations like the one that pushed Canadian cross-country skiier Beckie Scott to bronze at the Salt Lake City Games in 2002.

On race day Scott - a vocal proponent of cleaning up her sport - was elated to find herself on the podium, with a bronze medal around her neck.

But before the end of those Olympics, doping tests showed the two athletes who beat Scott had cheated and their medals were revoked. Scott was later awarded the gold.

Dr. Don Catlin is a veteran of the doping wars, having run the anti-doping operations at Salt Lake, Atlanta (1996) and Los Angeles (1984).

He says catching the cheaters before they compete is the better way to go about it.

"After the fact, you know, you do it, but it's much better to get it beforehand,'' says Catlin, a member of the IOC's Medical Commission and founder of Anti-Doping Research, Inc., a non-profit agency dedicated to combating doping in sport.

"And that's why they're doing so much more testing now before the Games. Right now the athletes are at risk to be tested in the Olympic context.''

And what percentage of athletes are at risk of being caught? Experts can only estimate how prevalent doping is in Olympic sports, though WADA Director General David Howman says the agency is involved in some studies aimed at getting a better handle on the scope of the problem.

Some people in anti-doping suggest about two per cent of athletes dope, Howman says, though a recent study in Germany put the number at eight per cent.

"It's of concern to us that the prevalence may be higher than what has been discussed over the years and we want to be alert to it,'' he says.

Some testing actually will have taken place before athletes leave their home countries, with positive drug tests leading to the occasional last-minute change in the lineups of Vancouver-bound squads.

Howman says between 70 and 80 athletes were scratched because of doping issue before the Beijing Games, though the Summer Olympics draw much larger numbers than do the Winter Games.

Last week Russia announced it was dropping cross-country skier Alena Sidko, a medal hopeful, from its Olympic team. There have been reports she tested positive for EPO at a recent race.

And in Vancouver, a flurry of testing will have started from last Thursday, when the Athletes' Village officially opened. Doping control for these games will operate out of a state-of-the-art facility set up in the Richmond Oval.