Environmental factors such as high fat content in a diet affect pro- and antioxidative balances in tissues. Our study was designed to determine whether a four-week diet enriched to a total of 15% fat content with either a polyunsaturated (linoleic) or saturated (palmitic) fatty acid predisposes or protects the liver tissue against oxidative stress in both non-diabetic and diabetic rats. In the rat liver the activity of catalase, superoxide dismutase, glutathione peroxidase, and the level of thiobarbituric acid reactive substances were determined. Our study suggests that both diets induce oxidative stress in livers of non-diabetic rats. However, in diabetic rats a diet enriched in linoleic acid appears to attenuate oxidative stress.