The relation among glutathione-related enzyme activities, thiobarbituric acid-reactive substances of the human aorta and internal mammary artery, and serum lipids was studied in 40 male patients undergoing coronary revascularization. Glutathione peroxidase and glutathione reductase activities were significantly higher in the internal mammary artery, whereas glutathione transferase activity was elevated in the aortic wall. Moreover, non-selenium-dependent glutathione peroxidase activity was detectable only in the aorta. The levels of thiobarbituric acid-reactive substances were significantly higher in the aorta. A positive correlation was found among the activity of glutathione peroxidase, glutathione reductase, and thiobarbituric acid-reactive substances in the internal mammary artery and total cholesterol, low density lipoprotein cholesterol, and triglycerides. In the aortic wall, a positive correlation among the activity of glutathione peroxidase, glutathione transferase, thiobarbituric acid-reactive substances, and the previously mentioned serum lipids was evident. In contrast, high density lipoprotein cholesterol was inversely related to enzymatic activities and thiobarbituric acid-reactive substances in both the internal mammary artery and aorta. In conclusion, significant differences in the levels of glutathione-related enzyme activities and thiobarbituric acid-reactive substances in the internal mammary artery and aorta were found, suggesting a different ability of the two tissues to counteract oxidative stress: the glutathione-related antioxidant properties and the level of lipid peroxidation in the arterial tissue seem to be specifically influenced by serum lipids.