We evaluated the efficacy of platelet scintigraphy using autologous platelets labeled with 111In-oxine, to assess the degree of arteriosclerotic activity in arteriosclerosis obliterans (ASO).Thirty-three patients with clinical signs of ASO, seen between January 1996 and August 1999, were enrolled in this study. Scintigraphic imaging results were compared with the findings of contrast angiography in 26 patients, 17 of whom were taking antiplatelet and/or anticoagulant drugs during the platelet imaging study.Angiography demonstrated atherosclerotic lesions at 38 sites from the abdominal aorta to the popliteal arteries in 23 patients. There was an accumulation of platelets at 17 of these sites (45%) and at 6 other sites without definite angiographic abnormalities. Lesions that resulted in less than 50% stenosis were detected slightly, but not significantly, less often than lesions with higher degrees of stenosis and occlusion (50% vs 30%, P = 0.73). The frequency of true-positive scintigraphic results was statistically higher in patients not taking antithrombotic agents than in those taking antithrombotic agents (70% vs 32%, P = 0.02).Our results suggest that imaging with 111In-oxine-labeled platelets may be useful for evaluating the pathophysiologic characteristics of atherosclerotic lesions in patients with ASO.