Arteriosclerosis of the right gastroepiploic artery (GEA) and the internal thoracic artery (ITA) were compared by pathological observation. Specimens were obtained from 35 patients who underwent coronary artery bypass grafting with simultaneous use of these two kinds of arterial grafts. Degree of arteriosclerosis was classified in five categories: 0, normal; 1, luminal narrowing less than 25%; 2, luminal narrowing between 25% and 50%; 3, luminal narrowing greater than 50%; and 4, overt atherosclerosis with ulceration or calcification. The number of arteries with degree 0, 1, 2, 3, and 4 was 16 (46%), 15 (43%), 3 (9%), 0, and 1 (3%) in GEA and 27 (77%), 8 (23%), 0, 0, and 0 in ITA, respectively. Incidence of degree 0 was higher in ITA, but differences were not significant. The mean wall thickness was 0.30 +/- 0.13 mm in GEA and 0.21 +/- 0.07 mm in ITA (p less than 0.05). In 23 patients who underwent postoperative angiography, all 46 arterial grafts were patent without focal stenosis. We conclude that GEA has slightly more intimal thickening than ITA, but significant luminal narrowing caused by arteriosclerosis is rare. Gastroepiploic artery can be expected to be a suitable conduit for coronary artery bypass grafting.