This study was designed to determine whether the treadmill exercise test (TET) causes a change in antioxidant enzyme activities and lipid peroxidation. TET was performed with 33 patients according to the Bruce protocol for the diagnosis of coronary artery disease (CAD). Blood samples were taken before the TET (BT), immediately after the TET (AT) and thirty minutes after the TET (AT 30 min). Lipid peroxidation of test positive (TP) patients was significantly increased AT and still increased AT 30 min. Superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase activities were also affected and decreased AT and AT 30 min. Lipid peroxidation and antioxidant ezyme activities were not chanced during the TET more than those BT in test negative (TN) subjects. In this study we observed that the lipid peroxidation was increased and the activities of antioxidant enzymes were decreased in patients in whom myocardial ischemia developed after the TET.