Recombinant human erythropoietin (rHuEpo) has now been in clinical trials for over four years. rHuEpo 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. rHuEpo has been shown to be effective in increasing the ability of individuals to donate blood for self-use and to increase the haematocrit in patients with rheumatoid arthritis. Preliminary results indicate that rHuEpo will decrease transfusion requirements of patients with the acquired immune deficiency syndrome who are anaemic. Trials in patients with anaemia associated with cancer or myelodysplastic syndromes are in early stages. rHuEpo will have a major impact as a therapeutic agent, particularly in patients with renal disease.