Mark Cavendish won his fourth stage in this year's Tour de France and Cadel Evans of Australia retained the overall lead Friday in a race reeling from a string of doping scandals.

The stage victory was the second in a row for the Team Columbia rider. Leading a group sprint, Cavendish beat Australia's Robbie McEwen in second by nearly two bike lengths, while Romain Feillu of France was third.

"The first stage win was my favourite. Today's was the hardest," Cavendish said of the hot and wind-swept trek along the 182-kilometre trek from Narbonne to Nimes.

"Every win's a win," Cavendish said.

Evans retained the yellow jersey by finishing alongside his main rivals in the main pack. He holds a one-second lead over Frank Schleck of Luxembourg and is 38 seconds ahead of U.S. rider Christian Vande Velde in third.

Earlier Friday, the Saunier Duval team fired Italian rider Riccardo Ricco, winner of the sixth and ninth stages. He was removed from the race Thursday after testing positive for an advanced version of banned blood booster EPO.

Ricco, who was runner-up in the Giro d'Italia this year, was the biggest name among three riders who tested positive for EPO at the Tour this year. The result prompted his Saunier Duval team to quit the Tour.

French judicial officials filed preliminary charges Friday against Ricco for alleged "use of a toxic substance," said Antoine Leroy, state prosecutor in the town of Foix. If convicted, Ricco could face up to two years in prison.

Ricco, who was held overnight by police, was released Friday and ordered not to speak to anyone from his team. Leroy said Ricco had contested the claim that he had used EPO.

A police search of a hotel room where Ricco had stayed turned up medical equipment, such as syringes, catheters and medical bags, but no doping products, Leroy said.

The head of France's anti-doping agency, Pierre Bordry, said that Ricco had tested positive for CERA, or continuous erythropoietin receptor activator, an advanced version of EPO.

Mircera, the brand name for CERA made by Swiss-based Roche Holdings, helps users produce more red blood cells, company spokeswoman Claudia Schmitt said. It received U.S. and European approvals last year as a treatment for anemia caused by kidney failure.

The substance remains much longer in the body than regular EPO.

Schmitt said Roche has provided information about the treatment to the World Anti-Doping Agency, which has banned EPO for use by athletes.

Spanish riders Moises Duenas Nevado and Manuel Beltran were also ejected from the Tour this year for using EPO.

Also Friday, Saunier Duval fired Leonardo Piepoli, an Italian who won the 10th stage of the Tour, for "violation of the team's ethical code." A team spokesman declined to elaborate.

Bordry said Piepoli was one of several riders targeted because he had suspicious blood parameters in pre-Tour blood tests July 4 and 5 and because of "information from outside sources." Bordry would not say what the sources were, adding only that he was awaiting test results on Piepoli and other riders.

A law went into effect in France this month that makes anyone who produces, transports, acquires or possesses doping products liable for up to five years in prison and a US$119,000 fine.

Before the new law went into effect, possession of a doping product was not illegal.

Some critics said the law was too tough, and that athletes should be punished with sports sanctions, not legal sanctions.