Erythropoietin (EPO) adjusts the red cell mass to the optimal size in order to satisfy the oxygen requirement of the body. The amount of circulating EPO is regulated by oxygen sensors in the kidney, which control the secretion of EPO through feedback signals. EPO stimulates the erythroid progenitor cells at different levels to develop into mature red blood cells. In anaemia, the serum EPO concentration, which is normally around 15 U/l, can increase 100-fold, or more. Patients with severe renal failure are unable to adapt the production of EPO in response to low haematocrit levels, and anaemia is due to a relative EPO deficiency. Studies have shown that recombinant human erythropoietin (r-HuEPO) could quickly correct anaemia in chronic renal failure by inducing a dose-dependent rise in haemoglobin and in the haematocrit level. r-HuEPO is now the standard treatment to correct severe anaemia in chronic renal failure. In recent years, r-HuEPO has been tested in other types of anaemia, some of which are fully discussed in this supplement together with various dosage regimens and routes of administration.