This is something of a catch-all term, says Don Catlin, a pharmacologist at the University of California, Los Angeles. Most of the time, people use it to describe a blood transfusion process that can improve athletic performance. The general idea is to take blood--either from yourself (an autologous transfusion) or--if you're in mid-Tour, say--from another, compatible donor (a homologous transfusion). You then concentrate it to separate the red blood cells, and inject it before a race. (Armstrong is accused of using the autologous method.) Either way, the extra red blood cells can increase endurance quite a bit--according to one study, improving stamina up to 34 percent. Erythropoietin (EPO), which was also mentioned in the allegations, is another way of increasing the concentration of red blood cells in your blood. It's a naturally occurring hormone, usually given to anemic patients, that can stimulate the body to create more red blood cells.