The determinations of cardiac troponin T provide the highest diagnostic efficiency for the detection of myocardial cell necrosis. To assess perioperative myocardial infarction, serum levels of cardiac troponin T were determined in 14 patients undergoing coronary artery bypass grafting (CABG). The patients were divided into two groups: group I (n = 9), those whose troponin T was less than 1.00 ng/ml on the first postoperative day; group II (n = 5), those whose troponin T was more than 1.00 ng/ml on the first postoperative day. Troponin T levels in group II patients were significantly higher than in group I from the second to the seventh postoperative day. Two patients in group II had specific changes on the electrocardiogram detecting perioperative myocardial infarction as a new Q wave and R wave reduction. These results suggest that troponin T is a valuable marker of perioperative myocardial infarction following CABG.