Vinokourov tested positive after showing his time trialling form on the way to victory in Albi on Saturday.
PAU, France -- Astana team leader Alexander Vinokourov failed a dope test after winning Saturday's Tour de France time trial, his team announced on Tuesday before quitting the race.
Vinokourov, who has won two stages in this year's race but was not in contention for the overall victory, has been sacked by Astana, the team said in a statement.
"The doping test carried on Alexander Vinokourov after last Saturday's time trial in Albi has returned positive," the Swiss team backed by Kazakh companies said in a statement.
"There is the presence of a double population of haematids (blood corpuscles), which implies there has been a blood transfusion with homological (the same type of) blood."
"Tour organisers have asked Astana Cycling Team to leave the race, which has been accepted spontaneously."
Vinokourov has asked for the B sample to be tested.
"I cannot comment on this until the result of the B sample's analysis," International Cycling Union (UCI) president Pat McQuaid told Reuters over the phone.
Tour de France director Christian Prudhomme said the cheats should now be worried.
"I told the riders before the start that this was a fantastic opportunity for renewal," he said at a news conference.
"That has failed. But the cheats must understand that they are playing Russian roulette. We are utterly determined."
Vuelta champion Vinokourov was one of the pre-race favorites for this year's Tour but injured his knees in a crash during the first week of the race.
The 33-year-old then blew any hopes of victory when he finished almost half an hour down on stage winner Alberto Contador and overall leader Michael Rasmussen on Sunday.
Vinokourov, who won Monday's 15th stage, was 23rd in the overall standings, 28 minutes and 21 seconds behind yellow jersey holder Rasmussen of Denmark.
Andreas Kloeden was Astana's best placed rider in the standings. The German, second in 2004 and third last year, was fifth overall, 5:34 down on the leader.
Astana sacked Matthias Kessler earlier this month after the German rider tested positive for the elevated levels of testosterone.
Eddy Mazzoleni, who finished third in this year's Giro d'Italia, quit Astana in July because of his involvement in a long-running Italian doping probe focusing on a doctor alleged to have supplied prohibited substances to athletes.
The rider denies any wrongdoing and is waiting to hear if he will be punished.
The team withdrew on the eve of the 2006 race after five of Vinokourov's team-mates were implicated in a doping scandal.
Last year's Tour de France winner Floyd Landis is still awaiting a ruling from a United States arbitration panel after testing positive for testosterone during the 2006 race.
The American has protested his innocence but if the decision goes against him, he could become the first Tour winner to be stripped of his title.
British rider David Millar, who was holding a news conference in Pau when the news of Vinokourov's positive test broke, said: "I'm speechless. It makes me sad. I have the impression the riders will never understand."
Millar served a two-year ban and was stripped of his gold medal from the 2003 world championships after admitting taking the banned blood-booster EPO.
On Saturday Vinokourov had decimated his rivals as he clocked one hour six minutes and 34 seconds for the 54 kilometers around Albi, one minute and 14 seconds quicker than second-placed Cadel Evans of Australia.
"I'm very happy with my performance. I'm very motivated," he said at the time. E-mail to a friend
Copyright 2007 Reuters. All rights reserved.This material may not be published, broadcast, rewritten, or redistributed.