Background: Increased lipid peroxidation (LP) and reduced enzymatic antioxidant defense have been observed in predialysis patients with advanced chronic renal failure (CRF) and in patients on maintenance hemodialysis (HD). To extend these observations, we evaluated the plasma, erythrocyte and dialysate levels of vitamins A and E and the plasma and dialysate levels of vitamin C as exogenous non-enzymatic antioxidants in children with CRF treated conservatively and on HD. The data obtained were related to LP monitored by erythrocyte malonyldialdehyde (E-MDA) and plasma organic hydroperoxide (OHP) concentrations. Patients: Forty-six predialysis children were enrolled in the study and divided into 2 groups: group I = moderate CRF (plasma creatinine <265.3 µmol/l), and group II = plasma creatinine ≧265.3 µmol/l. Group III consisted of 21 HD children. 27 age-matched healthy subjects served as a control group. Results: The plasma levels of vitamin A and vitamin C were significantly reduced in all CRF patients when compared to the controls, with the lowest values observed in children on maintenance HD (group III). Significant differences were also noted between the moderate CRF (group I) and HD (group III). Plasma levels of vitamin E were significantly decreased in moderate CRF (group I) and HD (group III) as compared to controls. In contrast, the erythrocyte vitamin A and vitamin E levels of predialysis children and HD patients were not different from the controls. The E-MDA and OHP concentrations in the 3 groups of CRF children were significantly higher than in healthy subjects. The concentration of plasma vitamin C was significantly inversely correlated with E-MDA, plasma OHP and creatinine in group I. In group II we found a significant correlation of plasma vitamin E levels with creatinine and E-MDA and a correlation of the plasma vitamin C concentration with E-MDA. Conclusion: CRF in children is associated with decreased concentrations of plasma antioxidant vitamins. This reduction is most expressed in children on maintenance HD and particularly concerns plasma vitamin C and erythrocyte vitamin E concentrations. The low levels of plasma vitamin A, E and C might result in reduced activity of the non-enzymatic antioxidant defense system and might be responsible for increased oxidative stress occurring in children with CRF.