Scanning electron microscopic evaluation of the resected plaques from 11 patients with symptomatic and asymptomatic lesions of the carotid artery bifurcation were carried out. The most common findings were mounds of atheromatous material, many of which appeared to be fractured and capped with fibrin-platelet exudates, projecting into the lumen of the vessels. Both small and large ulcer craters were identified, and attached bodies were present in three-fourths of the specimens studied. These consisted most commonly of platelet clumps and fibrin sheets and were intimately related to the atheroma.