ABSTRACT The purpose of this study was to examine the change in lipid peroxidation and antioxidant enzyme activities in healthy subjects and to evaluate the concentrations of superoxide dismutase, glutathione peroxidase and malondialdehyde, an end product of lipid peroxidation in exercise and smoking. Study included 257 appearently healthy individuals, 133 males and 124 females. In all subjects, malondialdehyde (MDA) levels were analyzed as an indicator of the lipid peroxidation activities. Superoxide dismutase, glutathione peroxidase activities were measured as an indicator of antioxidant activities. Oxidative stress was estimated by the method based on thiobarbituric acid reactivity. Erythrocyte superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities were estimated on hemolysates by use of commercial available kits (Randox lab., Dublin, Ireland). For all groups serum lipid peroxidation and erythrocyte SOD and GSH-Px were obtained at the initial and the following periods. Serum MDA level was higher in the elderly than in the children and in the adults. MDA levels were higher in the smoking, acute exercise than their counterparts in the control groups. GSH-Px activity was significantly lower in the acute exercise group, and higher in the trained group than those as controls. SOD decreased in the elderly, smoking and acute exercise groups and increased in trained individuals. There was a significant increase in lipid peroxidation activity and a significant decrease in antioxidant enzyme activity in cases of acute exercise and smoking as well as the elderly.