Early patency (two weeks) of 331 aortocoronary vein grafts was 89%. Late patency (one year) of 122 restudied grafts was 80%. A cumulative one year patency of 72% was calculated. Patency was similar for SV grafts, sutured distal to stenosis and segmental obstruction. Early patency was significantly decreased when the peroperative graft blood flow was 20 ml/min or less or the diameter of the recipient coronary artery was smaller than 1.5 mm. Cumulative one year patency was lower in symptomatic patients (54%) than in those who underwent consecutive reevaluation (80%). There was a trend towards improved patency rates for graft anastomosed to the left anterior descending coronary artery and grafts without pre-existing pathological changes. Patient parameters, such as at operation, sex, smoking habits, hypertension, lipid abnormalities, diabetes, previous myocardial infarction or depressed left ventricular function, had no bearing on patency. Graft failure occurring, despite refined surgical technique, is usually due to pathological changes of the vein graft per se or the recipient coronary artery and its vascular bed.