"People are defined by their principles and how they make their decisions," Landis said.
"To me, bicycle racing was rewarding by the pure fact that I was proud of myself when I put the work into it and I could see the results.
"It wouldn't serve any purpose to cheat and win the tour. I wouldn't be proud of it."
Landis was asked by his attorney Howard Jacobs if he used testosterone the night before stage 17 and replied: "No."
"Did you use any other banned substance that night?" Jacobs continued.
"No," Landis replied.
"Did you use testosterone or any other banned substance during the Tour de France?" Jacobs asked.
"No," Landis said.
Perhaps the biggest revelation from the trial so far has been that of three-time Tour de France champion Greg LeMond, who was allegedly taunted by one of Landis' associates in an anonymous telephone call about sexual abuse suffered in his childhood.
Even under the benign questioning of his own lawyer, Landis' one hour and 15 minutes on the stand did nothing to make that incident look any better.
Landis admitted that he himself was in the same hotel dining room with his friend and business manager Will Geoghegan when Geoghegan made the call, but said he didn't realise what was happening, and was appalled when he learned what Geoghegan had done.
The following day, LeMond said that he believed the call was a bid to stop him from delivering potentially damaging testimony of a phone call last August 6 in which, according to his recollection, Landis implicitly admitted doping.
"Of all the things that could happen to somebody, that's one of the worst," Landis said of the sexual abuse in LeMond's past.
"To make light of that is... I can't even put words to it."
The 31-year-old said LeMond had told him about the abuse in the same August 6 phone call, and he had discussed it with his defense team because he expected it to form part of his testimony.
He also didn't think it was particularly secret, because he said LeMond had told him he was writing a book about it.
Landis also disputed LeMond's recollection of the August 6 phone call, saying he never admitted cheating.
"I told him I didn't do it," Landis said.
"I told him it wouldn't make any sense for me to admit to something I didn't do."
Jacobs' questioning brought an end to the day's proceedings, but Landis will still face questioning by lawyers for the US Anti-Doping Agency (USADA) after the hearing resumes on Monday.