In present study, lipid peroxidation products (thiobarbituric acid reactive substances (TBARS) and diene conjugates (DC)) and markers of blood antioxidant status (serum antioxidative capacity (AOC) and red blood cells glutathione (RBC-GSH)) were measured to compare the extent of oxidative stress in 12 cardiac surgery and 10 septic general surgery patients. In heart surgery, arterial TBARS were significantly increased 15 min after the start and 15 min after cessation of cardiopulmonary bypass, while AOC at these times was decreased. Eighteen hours after surgery all parameters, except antioxidative capacity, had returned to preoperative levels. In septic patients, the preoperative level of lipid peroxidation was significantly higher and antioxidative capacity lower than in heart surgery patients. Surgery had no influence on oxidative stress markers in this group of patients. Increase in lipid peroxidation and reduction in blood antioxidant capacity, induced either by sepsis or cardiopulmonary bypass, were of comparable extent.