The importance of increase in the level of free oxygen species is well known in the development of complications during chronic renal failure. Insufficiency of antioxidant systems or increased production is responsible from high levels of oxidation products. Oxidative stress increases in dialysis treatment. In this study, the effects of hemodialysis (HD) and continuous ambulatory peritoneal dialysis (CAPD) on the levels of plasma malondialdehyde (MDA), an indicator of lipid peroxydation and the antioxidant system enzymes, erythrocyte glutation peroxydase (GPx) and superoxide dismutase (SOD) were investigated. 46 HD and 16 CAPD patients were included in the study. 24 healthy individuals were taken as controls. When compared with the HD group, plasma MDA levels were found to be significantly lower (p<0.05) and erythrocyte GPx and SOD levels were significantly higher (p<0.05, p<0.05) in the CAPD group. The MDA values of the both groups were significantly higher (p<0.0005, p<0.0005) while their GPx and SOD values were significantly lower (p<0.0005, p<0.0005, p<0.0005, p<0.0005) in respect to the control. It was concluded that when the parameters of oxidant and antioxidant systems were investigated both dialysis applications significantly increased oxidative stress. However, perito