Recombinant human erythropoietin (rhEPO), which increases red cell mass, is one of the most abused substances in sport. Abuse is currently undetectable by the only direct routine method, immunoassay, since blood and urine rhEPO are immunologically indistinguishable from endogenous EPO. Elevated EPO levels are only detectable several days after rhEPO administration. Indirect parameters have therefore been introduced, primarily the haematocrit level, but also markers of functional iron deficiency during or after rhEPO administration (hypochromic red cells and reticulocytes, serum transferrin receptors, ferritin levels) and, in the urine, fibrin degradation products. Although iron status indices have yielded promising results, athletes are currently banned solely on the basis of their haematocrit. Yet various factors can cause false positive haematocrit results with potentially fatal consequences to athletes' careers. Until new direct assays such as liquid chromatography-mass spectrometry have been evaluated and introduced, efforts must be directed at using a battery of tests to increase the sensitivity and specificity and reduce the number of false positives and false negatives.