I'm not a doctor and I wish a doctor Freeper would comment, but isn't it true that you can get surges of testosterone from weight-lifting, sex, etc? It seems plausable to me that after Landis mind-boggling stage 17 performance his system would be flooded with the stuff.
Having said that, its not like Testosterone would give you a one-shot boost. So he didn't win stage 17 due to Testosterone, any more than he didn't win most of the previous stages, due to Test. You could expect a one-shot boost from an amphetimine (banned), or ephedra(banned), alot of caffeine (which they are allowed to drink), and who knows, maybe EPO or blood doping. The effects of Test take a week or two (at least) to notice. That said, he COULD have been using Test for a while, but I thought they already tested for that before the race..?