['Atherosclerosis may be regarded as an inflammatory disease dominated by macrophages. We tested whether macrophages in carotid artery atherosclerotic plaques are associated with echolucency on B-mode ultrasound imaging, lipid levels, inflammatory markers, and aspirin use.', 'We studied 106 patients undergoing carotid endarterectomy having >/=50% carotid artery stenosis and previous ipsilateral hemispheric neurologic symptoms.', 'Macrophages were particularly common in plaques with a high content of lipid and hemorrhage and, conversely, rare in plaques dominated by calcification and fibrous tissue. Macrophage density in carotid artery plaques classified by B-mode ultrasound imaging as echolucent (n = 56), intermediate (n = 25), or echorich (n = 25) was 1.8% +/- 0.2%, 1.5% +/- 0.4%, and 1.0% +/- 0.2% (+/-SE), respectively (analysis of variance, P =.02). A computer-generated measure of plaque echolucency, gray-scale median, was associated with increased macrophage density (r = -0.31; P =.002). Furthermore, plasma and low-density lipoprotein cholesterol levels were associated with carotid artery macrophage density (r = 0.26, P =.008 and r = 0.23, P =.02); this was most pronounced in patients with lipid-rich plaques. Macrophage density was not associated with plasma levels of acute-phase reactants. Finally, macrophage density in carotid artery plaques of users (n = 55) and nonusers of aspirin (n = 51) was 1.2% +/- 0.2% and 1.8% +/- 0.2% (t test, P =.01).'] Are macrophages associated with lipid-rich carotid artery plaques , echolucency on B-mode imaging , and elevated plasma lipid levels?