Erythropoietin is the primary growth factor for red blood cells. A glycoprotein hormone synthesized by the kidneys, erythropoietin serves to increase red blood cell production in response to tissue hypoxia. It exerts its effect by increasing the numbers of erythroid progenitor cells in the bone marrow, and by increasing the rate at which their development is accomplished. With the introduction of recombinant erythropoietin in 1987, an important pharmacological agent became available for the manipulation of erythropoiesis. While used primarily for the treatment of the anemia of renal failure, recombinant erythropoietin has also shown usefulness in treating other types of anemias in which the endogenous erythropoietin response is insufficient. Perioperative use of the drug grew as a natural extension of this, and erythropoietin has been applied to correct preoperative anemia, augment autologous blood donation, and improve postoperative red cell recovery. Analysis of these perioperative clinical studies reveals success in these areas, but it also reveals that closer attention to the physiology of the natural response, and to the pharmacology of the recombinant product, might significantly improve results. Such an improvement in efficacy is both desirable and necessary when use of the drug is viewed in the setting of today's changing health care environment. By optimizing dosing schedules and targeting the drug to those most at risk for red cell transfusion, recombinant erythropoietin will likely become an important tool in efforts to achieve the elusive goal of bloodless cardiac surgery.