Of sixty-four acute myocardial infarcts showing myocardial necrosis within 5 days after onset, 37 had fresh coronary occlusive thrombi with recent thrombus in the deep layer. The recent thrombi were usually located in the severely stenosed segment of arteriosclerotic coronary arteries. They adhered to the intima not only near but on the opposite site to the plaque ulcers and sometimes covered the ulcer. In two thirds of the cases, both the recent thrombi and plaque ulcers were located in the same segment. In the others, the topographical relationship of plaque ulcers to recent thrombi in the longitudinal direction varied from one case to another. These findings show that the recent thrombus might play an important role in the formation of a fresh occlusive thrombus and plaque ulcer of coronary arteriosclerotic lesions.