PARIS — More than 500 doping tests, including targeted checks, will be conducted before and during the Tour de France, says the head of the cycling union.

A group of 50 targeted riders, considered as race favorites or whose biological passport data have raised suspicion, will be under more scrutiny, International Cycling Union chief Pat McQuaid said Wednesday.

"From the numbers of tests, in my opinion, it will be the most tested event in the history of sports," McQuaid said. "It's enormous."

Last year's Tour de France was marred by a string of doping charges. Six riders tested positive during the race or in retroactive checks.

McQuaid spoke at a news conference with Pierre Bordry, the head of the French anti-doping agency (AFLD). The UCI and the AFLD will work together on the Tour, having already collaborated at the beginning of the season during the Paris-Nice race.

"What's important, is not the number of tests but the fact that we target riders", Bordry said.

The biological passport has been used to monitor more than 850 professional riders since it was created with the World Anti-Doping Agency and launched in January 2008.

Each rider has given a series of blood and urine samples, which helped to create an individual body chemistry profile using analysis designed by a WADA-accredited laboratory in Lausanne, Switzerland.

Riders will be tested while training before the race. Two days before the three-week race, which begins July 4, all riders will give two blood samples that will be tested and stored.

"Many samples taken in the Tour will be stored for future analysis," said McQuaid of substances that are currently undectable.

During the event, testers will be able to detect the blood-boosting hormone CERA, and insulin, UCI doctor Mario Zorzoli said.

"Between eight and 11 riders will be tested every day on the basis of their sporting results, but also on the basis of our targeting policy," Zorzoli said.

After each stage, some riders will be chosen at random for checks.

Last year, Austrian cyclist Bernhard Kohl was accused of doping. He retired after admitting he had used CERA, and has criticized the efficiency of the biological passport.

"I've invited him to come and see us at the UCI headquarters in Aigle," McQuaid said. "If he has information to share with us, he is welcome. But when he comes, we will show him his biological passport and I'm sure his opinion will change afterward."

McQuaid also announced the start of disciplinary proceedings against a "certain number of riders" based on suspicious data on their biological passport.

He declined to name the riders but pledged to do so early next week, once the riders, their teams and national federations have been informed. He said that none of the cyclists would get a provisional suspension and it would be "up to the teams" and federations to take action.

With the biological passport, suspected doping offenses are spotted in fluctuations from the athlete's known baseline levels — in effect, searching for the evidence of doping rather than specific illegal substances.

However, the UCI has hesitated in bringing a disciplinary case based solely on passport evidence because of fears the entire process could be challenged in court.