MARK Cavendish of Britain won his fourth stage in this year's Tour de France and Australia's Cadel Evans retained the overall lead yesterday morning 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 favorite. Today's was the hardest,'' Cavendish said of the hot and wind-swept trek along the 182km from Narbonne to Nimes. ''Every win's a win.''

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

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

Ricco, who was runner-up in the Giro d'Italia this year, was the biggest name among three riders who have 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 on Friday against Ricco for alleged ''use of a toxic substance,'' state prosecutor in the town of Foix, Antoine Leroy said. If convicted, Ricco could face up to two years in prison.

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

Police found medical equipment, such as syringes and catheters, but no doping products, in Ricco's hotel room 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. It received US 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.

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

Also yesterday, 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 on July4 and 5 and because of ''information from outside sources''. Bordry would not say what the sources were, but said he was awaiting test results on Piepoli and other riders.

A law came 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 $A122,000 fine.

Before the new law possession of a doping product was not illegal.

AP