In anaemia of chronic renal failure, the most important factor in the shortened erythrocyte survival may be lipid peroxidation of the cell membrane. Defective antioxidant activity may increase this damage. Although recombinant human erythropoietin (r-HuEPO) can effectively correct anaemia in chronic haemodialysis patients, its actions on lipid peroxidation and antioxidant activity are not clear. These actions were investigated in 13 patients undergoing chronic haemodialysis. Antioxidant activity, including red blood cell superoxide dismutase and total glutathione peroxidase levels and the lipid peroxidation product malondialdehyde, were measured before and 3 months after initiation of r-HuEPO treatment, using heparinized venous whole blood for cell and plasma determinations. Age-matched healthy volunteers were controls. Significantly higher levels of superoxide dismutase and total glutathione peroxidase were found in the patients than in the controls (p < 0.01). Plasma malondialdehyde levels were not affected by r-HuEPO. The results are explained by erythropoiesis and cellular haemoglobin synthesis due to r-HuEPO, followed by increase of circulating young red cells. The membranes of these young cells contain more antioxidant enzymes than the others. Despite r-HuEPO treatment, plasma malondialdehyde levels in haemodialysis patients may be higher than normal because of the uraemic milieu and the chronic haemodialysis.