Landis had always denied using banned substances, but this week told the Wall Street Journal that he did indeed cheat, as did Lance Armstrong and three other American cyclists.
Armstrong is currently competing in the Amgen Tour of California. Reporters tracked him down Thursday morning in Visalia where the fifth stage of the race starts. Armstrong later crashed and went to the hospital for eight stitches under one eye.
Armstrong denied the allegations and painted Landis as an opportunist who's been harassing him for years.
"I don't want to make a personal attack on Floyd Landis. I don't think he's a good guy or a bad guy. I think he certainly has some issues," Armstrong told reporters Thursday morning. "You have somebody that's been under oath several times with a completely different version. You have somebody that's written a book with a completely different version. He has nothing. He's got no proof. It's his word versus ours. We like our word."
Landis was the first person to be stripped of a Tour de France title. He claims that Armstrong and longtime coach Johan Bruyneel paid an International Cycling Union (UCI) official to cover up a test in 2002 after Armstrong purportedly tested positive for the blood-boosting drug erythropoietin, or EPO. The UCI, however, denied changing or concealing a positive test result.
In an e-mail Landis sent to USA Cycling Chief Executive Steve Johnson, he said Armstrong's positive EPO test was in 2002, around the time he won the Tour de Suisse. Armstrong won the Tour de Suisse in 2001 and did not compete in 2002.
"We're a little confused, maybe just as confused as you guys," Armstrong said, with Bruyneel by his side. "The timeline is off, year by year."
Landis also implicated other cyclists, including longtime Armstrong confidant George Hincapie and Olympic medalist Levi Leipheimer, and acknowledged using human growth hormone starting in 2003. The Wall Street Journal reported another e-mail from Landis also linked another top American racer, Dave Zabriskie, to doping.
Hincapie said he was "really disappointed" by the allegations. Jim Ochowicz, a former top USA Cycling official, who was also implicated by Landis, defended himself and Hincapie.
"These allegations are not true, absolutely unfounded and unproven," said Ochowicz, now the president of BMC Racing, Hincapie's current team. "This is disappointing to anyone who works in the sport or is a fan of the sport."
The Associated Press contributed to this report.