Mark Cavendish of Britain won the 12th stage of the Tour de France yesterday, hours after cycling's showcase race was thrown into chaos with a third doping bust this year -- netting the biggest name yet.

Cavendish earned his third stage win this year by leading a group sprint after the trek through rolling hills and plains for the 168.5-kilometer ride from Lavelanet to Narbonne.

Cadel Evans of Australia retained the overall leader's yellow jersey, trailing in the main pack. He has a one-second lead over Frank Schleck of Luxembourg and a 38-second lead over American rider Christian Vande Velde.

Cavendish, a Team Columbia rider who had never won a Tour stage before this year, outpaced Sylvain Chavanel of France in second and Gert Steegmans of Belgium in third.

But the race was badly overshadowed by the latest doping case.

Italian rider Riccardo Ricco was detained by police and booed by spectators before the stage began, becoming the third person this year to test positive for performance enhancer EPO - cycling's most famous drug.

Ricco's Saunier-Duval team withdrew from the Tour and suspended all of its activities after news of the rider's test. For the third straight year, the race has been marred by doping.

With Ricco and his teammates out, Italian Vincenzo Nibali of Liquigas took the white jersey for the best young rider and German Sebastian Lang of Gerolsteiner the polka dot jersey for best climber.

Ricco, a 24-year-old Italian who won two Tour stages this year, tested positive for the performance enhancer after the fourth stage, a time trial in the western town of Cholet.

Pierre Bordry, the head of the French anti-doping agency, announced the result, leading to the team's withdrawal shortly before the start of the 12th stage.

"It's a team decision not to start the race," Saunier Duval sporting director Matxin Fernandez said. "He's our leader, we can't act as if nothing happened.

"We suspend the activities of the team until we know what happened," Fernandez added.