Adult male New Zealand white rabbits were fed for 3 months a stock diet supplemented with 6% (w/w) soybean oil heated at 240 degrees C for 60 min. After the first month of treatment a significant increase in total lipid content of serum was observed mainly due to the cholesterol ester fraction. Simultaneously, grossly induced atherosclerosis and marked liver damage were histologically and clinically demonstrated. Lipid peroxide values, performed by thiobarbituric acid test in lipid extracts from liver, aorta and bile showed a significant increase as compared to controls. Lipoperoxidation rate increased with the duration of feeding. Parallel to this there was a marked reduction in the activities of glutathione peroxidase, superoxide dismutase and catalase in liver and aorta, all enzymes involved in the mechanism of detoxification of lipid peroxides. The results are in agreement with the hypothesis that lipid peroxidation can play a significant role in the pathogenesis of atherosclerosis.