Reduced and oxidized glutathione and pyridine coenzymes, glutathione-related enzymes and CuZn-superoxide dismutase (CuZn-SOD) were investigated in the RBC of patients with chronic renal failure (CRF) and in age- and sex-matched controls. The effects of hemodialysis (HD) were also studied. A defective RBC redox state was shown in the CRF group based on a decreased GSH/GSSG ratio and NADPH levels. Increased activities of glutathione transferase (GSH-S-T) and CuZn-SOD were observed before HD. Dialysis apparently restores the levels of antioxidant enzymes and at the same time strongly affects the redox state. Thus we can speculate that HD can generate severe redox impairment inducing damage in RBC and plasma antioxidant enzymes. Increased erythrocyte GSSG and GSM-S-T levels coupled with a reduced hexose monophosphate shunt (HMPS) function may be useful indexes of oxidative stress in uremic anemia.