Background: Free radical-mediated changes are thought to be involved with atherosclerosis in patients with chronic renal failure. Methods: The protein carbonyl and malondialdehyde (MDA) levels in serum as the markers of radical-induced protein and lipid oxidations were measured in chronic renal failure patients. Results: Serum carbonyl and MDA levels in both hemodialysis and peritoneal dialysis patients were not found to be different as compared with healthy subjects. In both patient groups, the approximately twofold increment in total antioxidant activity (ferric reducing/antioxidant power; FRAP) and uric acid values in serum were found. The high uric acid levels in both patient groups might be partly responsible for the increment in FRAP values. In addition, all patients received multivitamin preparations including ascorbate, which was also a major antioxidant in serum. Conclusions: Our data suggest that oxidative stress does not become the major threat for patients with chronic renal failure. The increment in endogenous and exogenous antioxidant capacities in serum might be thought to prevent any possible radical-induced damage in patients with chronic renal failure. In addition, the increased nitric oxide (NO) levels especially in hemodialysis patients might likely favor an antioxidant effect. (C) 2002 Elsevier Science B.V. All rights reserved.