Lance Armstrong insists he has nothing to hide despite allegations of performance-enhancing drug use made by Floyd Landis.
Landis, who was stripped of the 2006 Tour de France title, admitted drug offences of his own earlier this week.
The 34-year-old American has now sparked a media storm after making a series of allegations in e-mails to cycling and anti-doping officials.
Landis has implicated a number of riders and team officials in his e-mails, including Armstrong and his long-term team boss Johan Bruyneel.
The former US Postal team-mate of Armstrong has alleged that he and Bruyneel struck a deal with authorities to conceal a positive drugs test during the 2002 Tour of Switzerland.
However, the UCI, cycling's governing body, has reacted with incredulity after revealing the seven-time Tour de France champion did not even compete in the event.
Speaking ahead of pulling out of the Tour of California after a crash during Thursday's fifth stage, a relaxed Armstrong said: "I have nothing to hide. I think history speaks for itself here.
"It's our word against his word. I like our word. We like our credibility.
"Floyd lost his credibility a long time ago."