The pathophysiology of the anemia of chronic renal failure (CRF), erythropoietin physiology, the characteristics of recombinant human erythropoietin, and the results of nearly 2 years of therapy with this product in hemodialysis patients are detailed in this review. This anemia is primarily an endocrine deficiency state corrected by the hormone erythropoietin. Correction of the anemia eliminates transfusions and their associated risks, improves physical endurance, and results in healthier patients beginning dialysis. Adequate support services will be necessary to maximize patient rehabilitation and employment potential. Further research is needed to better understand erythropoietin physiology and metabolism, and the impact of uremia on end organ function in the absence of anemia.