Recombinant human erythropoietin has become an essential part of the management of anemic patients with end-stage renal disease. It is also used to treat the anemia associated with cancer and other diseases, and it improves quality of life. In recent years, studies in animals and humans have focused on the use of rHuEPO for other indications. It has been found to play a role in both cardioprotection and neuroprotection. It has effects on the immune system, and can cause regression in hematologic diseases such as multiple myeloma. It may also improve the response of solid tumors to chemotherapy and radiation therapy. On the other hand, concerns have been raised following two studies of patients with solid tumors in whom those treated with rHuEPO had diminished survival. Criticism of the design of these studies makes it clear that large, well-designed, randomized trials must be performed to determine the role of rHuEPO in the treatment of cancer, and more generally to clarify the full clinical benefits of the drug, while minimizing the harm.