The erythrocyte is a highly specialized cell whose main functions are oxygen transport and the mediation of carbon dioxide transport. Energy production in the mature erythrocyte depends on glycolysis, with glucose as the principal substrate. Glycolysis and the oxidative pentose phosphate pathway generate NADH and NADPH to reduce methemoglobin, which is being continuously produced, and the antioxidant glutathione, which is present in high concentrations. Red blood cells are equipped with a highly effective antioxidant defense even without the glutathione system. Compared with other cell types, they possess high activities of the most important antioxidant enzymes. Most of the nonenzymatic antioxidant capacity of whole blood is likewise localized in the erythrocytes. Circulating red cells are mobile free radical scavengers and provide antioxidant protection to other tissues and organs. An imbalance between pro-oxidant reactions and antioxidant defense is described in patients with chronic renal failure. Oxidative stress increases as antioxidant defenses are weakened by pro-oxidant hemodialysis factors; it increases further still in renal anemia with a very low red cell count. Thus in terms of free radical metabolism, the only arguments remaining over the complete correction of renal anemia are those in favor, with none against.