American cycling's governing body has described doping allegations against Tour de France legend Lance Armstrong as "completely without credibility".
French paper L'Equipe claimed signs of EPO were found in samples of the seven-time Tour de France winner's urine from the 1999 race.
Armstrong denied the claims and said the article was part of a "witch hunt".
"Preposterous is a strong word, but it is warranted in this case," said Gerard Bisceglia, boss of USA Cycling.
"Lance Armstrong is one of the most tested athletes in
the history of sport and he has come up clean every single time.
"This kind of years-ago testing of a single sample with new technology is completely without credibility.
"What's worse is that Lance cannot defend himself because there is no mechanism for final resolution."
Earlier this week, the boss of the World Anti-Doping Agency (Wada) said the organisation is looking into the doping claims against Armstrong.
Wada president Dick Pound said: "It's a pretty serious story if it is true.
"We've not decided what we'd do because I've not looked at all the details."
Pound said Wada would not be able to make a judgement until it had seen all the evidence.
"We will look at the information available and then we will decide the best way to get as much light on this as possible," he said.
Tests on the samples from the 1999 race were carried out in 2004 because cycling's governing body did not start using a urine test for EPO until 2001, L'Equipe said.
Pound said the issue is a matter for the International Cycling Union (UCI) and USA Cycling, noting that Wada had not yet been formed when the samples were taken.
"But what is good for me is it's a lesson to anybody using drugs that we may not catch you on day one, but sooner or later, the truth will come out," said Pound.
"Now the riders involved have a serious responsibility to explain how it is that the substance got into the system."
Wada was launched in November of 1999, four months after the samples would have been taken from Armstrong during his first Tour de France triumph.