Apolipoproteins from human plasma high density (HDL), low density (LDL) and very low density lipoproteins (VLDL) were visualized in human arteries employing immunofluorescence techniques. Comparison between the localization patterns in extracranial and intracranial arteries and those in coronary arteries and the aorta was made. ApoA-I from HDL, apoB from LDL, and apoCIII from VLDL, as well as neutral lipid, were all localized to connective tissue and extracellular lipid pools in atherosclerotic lesions, and only to areas of intimal thickening in grossly "uninvolved" arteries. The degree of superposition of localizations was similar in each vascular bed, and within the error resulting from the structural changes due to the focal nature of the atherosclerotic process. These results suggest a broad specificity in localization of apolipoproteins in most arterial lesions, and suggest that no differences in apolipoprotein accumulation exist between extracranial and intracranial arteries, coronary arteries, or the aorta. Variations in prevalence for atherosclerosis in each arterial bed must be accounted for on other bases.