The efficacy of contrast-enhanced computed tomography to define graft patency status was studied in 42 patients with 100 aortocoronary vein grafts. The status of each graft had been determined earlier by angiography. A rotary fan beam whole body scanner with a 2 second scan duration was used. Initial scans determined the optimal level for study of the graft; patency was assessed by computed tomographic enhancement of the graft after intravenous bolus injection of 30 ml meglumine and sodium diatriazoate. The computed tomographic studies were evaluated without knowledge of the angiographic findings; graft status by computed tomography was interpreted as patent, occluded or equivocal. Overall, computed tomography correctly defined graft patency status in 79 of the 100 grafts and incorrectly identified it in 9; in 12 grafts, the computed tomographic diagnosis was equivocal. Computed tomography correctly identified 61 of 74 patent grafts and 18 of 26 occluded grafts. Patency status was correctly defined by computed tomography in 35 of 37 grafts to the left anterior descending artery, 23 of 30 grafts to circumflex branches and 19 of 31 grafts to the right coronary artery. These data indicate that computed tomography is a promising noninvasive method of determining patency of aortocoronary bypass grafts, especially of grafts to the left anterior descending artery.