Recombinant human erythropoietin (rhEPO) has now been in clinical trials for over three years. It has been shown to be nearly uniformly effective in correcting the anaemia of patients on haemodialysis or patients with progressive chronic renal failure not yet on dialysis. Preliminary results indicate that rhEPO is effective in increasing the ability of individuals to donate blood for self-use and early trials have shown the drug to increase the haematocrit in patients with rheumatoid arthritis. Trials in patients with anaemia associated with cancer or myelodysplastic syndromes are warranted. rhEPO will have a major impact as a therapeutic, particularly in patients with renal disease.