The course of 146 consecutive patients with significant occlusive disease of the left main coronary artery who underwent coronary artery bypass surgery during a 4 year period is reviewed. Preoperatively, 11 patients were in New York Heart Association functional class II, 57 in class III and 78 in class IV. Seventy patients had progressive angina and 12 unstable angina. There were two operative deaths (surgical mortality rate 1.4 percent). Seven patients (4.8 percent) had a perioperative acute myocardial infarction. Complete follow-up has been achieved in the surgical survivors over an average period of 18.1 months; 77 percent of the surviving patients are completely asymptomatic and 19 percent are in functional class II. Four patients (2.8 percent) had a nonfatal late postoperative myocardial infarction and five (3.5 percent) died during the late postoperative period (3.3 percent annual mortality rate during a 2 to 47 month follow-up period). Postoperative cardiac catheterization studies performed in 35 patients an average of 12.1 months postoperatively revealed 78 percent of 80 grafts and patency of at least 1 graft in 93 percent of patients. Results of 42 (89 percent) of 47 near maximal treadmill stress tests were abnormal preoperatively compared with results of 14 (26 percent) of 54 postoperatively; in 74 percent of patients having both a preoperative and postoperative stress test, abnormal preoperative test results converted to normal after surgery. This study suggests that direct myocardial revascularization may offer an effective means of improving both the quality and duration of life in a patient with significant occlusive disease of the left main coronary artery.