From May 1988 to March 1990, the bovine internal thoracic artery (ITA) graft, 3 mm in diameter, was used for coronary artery bypass grafting in 29 patients with the approval of the Japanese Ministry of Health. Excluding three postoperative deaths and 6 patients who rejected postoperative angiography, 20 patients (13 men and 7 women; mean age, 62 years; range, 37 to 80 years) were followed up angiographically for up to 4 years. Sites of bovine ITA anastomosis were as follows: anterior descending, 4; circumflex, 5; and right coronary artery, 11. The mean bovine ITA graft blood flow measured by electromagnetic flowmeter was 75.2 mL/min (range, 40 to 150 mL/min). During the mean follow-up of 45 months (range, 30 to 52 months), 12 patients underwent postoperative angiography once, 6 patients twice, and 2 patients three times. It revealed 14 of 16 (88%) bovine ITA grafts were patent within 2 posioperative months. Three of 6 (50%) were patent at 3 to 12 months, of which 2 patent grafts required balloon angioplasty for distal anastomotic stenosis. In 7 patients restudied later than 1 year (20, 24, 25, 44, 48, 50, and 52 months), one of seven grafts (14%) was patent. There was stenosis (≤50%) at four distal and one proximal bovine ITA anastomotic sites, but no focal stenosis was found in the trunk at any period. There was one late death due to renal failure, one myocardial infarction, and one mild angina due to bovine ITA graft failure. The patency rate of concomitantly used autologous grafts was 93% ( 14 / 15 ) in ITA, 100% ( 4 / 4 ) in gastroepiploic artery, and 94% ( 17 / 18 ) in saphenous vein. In conclusion, the bovine ITA graft is not suitable for coronary artery bypass grafting at present because the occlusion rate greatly increases with time.