Landis states the he used EPO (erythropoietin) to increase his hematocrit to improve performance during cycling events.(EPO is pictured here.)
He has also stated that Lance Armstrong, another champion cyclist, gave him EPO and discussed his own blood doping experiences with Landis. Armstrong denies these claims.
Listen to the story from NPR:
I have an article on doping at The A&P Professor website that includes a lot of resources, as well as tips on using the topic of doping to engage students in a deeper understanding of human structure and function.
The A&P Professor, accessed May 21, 2010
[Tips and resources regarding doping for A&P courses.]