The frustrating part is that recombinant human (rh) EPO is very difficult to detect - it's extremely close in structure to the EPO that we all produce naturally. That means that, when administered carefully, rhEPO it won't ilicit much if any immune response so there are few antibodies to detect. Plus, EPO itself is a fairly short-lived molecule in the bloodstream; biotech companies (including my fine employer) nowadays actually try to make derivatives of these kinds of molecules in order to prolong their lifetimes in the bloodstream (and hence increase their efficacy) - obviously such products won't be of any interest to the cheaters in the sporting community!

But lacking any sensitive, reliable, reproducible test, it's going to come down to one man's word over another ...