Six chronic uremic patients on regular hemodialysis treatment were given recombinant human erythropoietin (r-huEPO) in a dose of 50 U/kg of body weight intravenously thrice weekly for 14 weeks. Following r-huEPO therapy, unstimulated whole blood superoxide anion (O2) generation did not change significantly, while opsonized zymosan-stimulated whole blood O2 generation increased. At the same time, erythrocyte superoxide dismutase and, in particular, glutathione peroxidase activities were found to be reducing with concomitant lowering of erythrocyte malonyldialdehyde (MDA) concentrations and increase in plasma MDA concentrations.