Lance Armstrong has recently been "stripped" of his Tour de France titles by the USADA. They state, among other allegations:
(1) Use and/or attempted use of prohibited substances and/or methods including EPO, blood transfusions, testosterone, corticosteroids and masking agents.
Additionally, scientific data showed Mr. Armstrong’s use of blood manipulation including EPO or blood transfusions during Mr. Armstrong’s comeback to cycling in the 2009 Tour de France.
The world cycling body has not made any similar allegations and Lance Armstrong maintains that he is the 'most tested athlete ever' and that he never failed a drug test.
It seems that the test for EPO is fairly new, being invented and first used around the year 2000:
A test for EPO didn't exist until 2000 and wasn't successfully used to catch doping until the 2002 Olympics. The accuracy of the procedure is getting better, but still has flaws. A 2008 study sent identical blood samples to two World Anti-Doping Agency (WADA) labs, and the labs came back with completely different results. In one case, Lab A reported that all eight samples were positive for EPO doping, while Lab B found that all eight were negative.
People have even alleged that Lance himself admitted using EPO when asked about it in the 1990s, but he strongly denies these allegations.
What is the evidence indicating that Lance Armstrong used EPO during his cycling career?