The United States Anti-Doping Agency said today it is stripping US cyclist Lance Armstrong of his seven Tour de France titles and banning him for life.
Mr Armstrong indicated late last night that he would not challenge the USADA's charges that he had doped throughout his career, saying "enough was enough" but denying he had ever used performance-enhancing drugs.
The ban is retroactive to 1 August 1998, through the present and includes all seven of his Tour de France victories.
Mr Armstrong, a cancer survivor considered one of the all-time greats in his sport, made his announcement yesterday in a written statement as he faced a midnight deadline to formally challenge the accusations against him.
On his website he said: "There comes a point in every man's life when he has to say, 'Enough is enough'."
"For me, that time is now. I have been dealing with claims that I cheated and had an unfair advantage in winning my seven Tours since 1999."
USADA Chief Executive Travis Tygart said: "It is a sad day for all of us who love sport and our athletic heroes.
"This is a heartbreaking example of how the win-at-all-costs culture of sport, if left unchecked, will overtake fair, safe and honest competition, but for clean athletes, it is a reassuring reminder that there is hope for future generations to compete on a level playing field without the use of performance-enhancing drugs."
Mr Armstrong, who retired from professional cycling last year, has long denied that he used performance enhancing drugs to help fuel his brilliant career.
He maintained that emphatic denial in the statement issued yesterday, stressing that there was no physical evidence to support what he called Mr Tygart's "outlandish and heinous claims".
Mr Armstrong, who never failed a doping test, said he would "jump at the chance" to put the allegations to rest once and for all, but refused to participate in the USADA process, which he called "one-sided and unfair".
He disputed the agency's authority to take away his titles.
"Today I will turn the page," he said. "I will no longer address this issue regardless of the circumstances."
World Anti-Doping Agency President John Fahey said: "He had a right to contest the charges. He chose not to.
"The simple fact is that his refusal to examine the evidence means the charges had substance in them."
The USADA, a quasi-governmental agency created by the US Congress in 2000, formally charged Mr Armstrong in June with doping and taking part in a conspiracy with members of his championship teams.
Five other cyclists have been accused of conspiring with Mr Armstrong over the course of 14 years to hide doping activity.
The agency said in a letter to Mr Armstrong that it has blood samples from 2009 and 2010 that are "fully consistent" with doping.
In the letter, which was published in the Washington Post, the agency said it also has at least ten former teammates and colleagues of Mr Armstrong who will testify he used doping drugs during races from 1999 to 2005.
Former teammate and deposed Tour de France winner Floyd Landis accused Mr Armstrong in 2010 of not only using performance-enhancing drugs but teaching others how to avoid being caught.
Mr Landis said he witnessed some of his teammates, including Mr Armstrong, use illegal drugs to boost performance and endurance.
Earlier this month, a federal judge dismissed Mr Armstrong's effort to block the inquiry, despite a contention by his attorneys that USADA gathered evidence by threatening to ruin the careers of fellow cyclists who have agreed to testify against him.
Mr Armstrong's lawyers also argued that the agency's rules violate his right to a fair trial and that it lacks proper jurisdiction to charge him.
In February, the Justice Department dropped an investigation centred on whether Mr Armstrong and his teammates cheated the sponsor of their bike racing team, the US Postal Service, with a secret doping programme.
Mr Armstrong's attorneys said he had "passed every drug test ever administered to him in his career – a total of 500 to 600 tests ... more drug tests than any athlete in history".
They say the International Cycling Union has proper jurisdiction in the case.