Well-resolved proton (1H) NMR spectra of solid human arterial plaque can be acquired. Studies have been carried out of human fatty plaque obtained postmortem (ex vivo), the total lipids extracted from human atheroma, and a model mixture of cholesteryl esters whose lipid composition resembles that of human atheroma. In each case, well-resolved 1H NMR spectra were obtained at body temperature (37 degrees C), with little or no underlying broad signal. Such sharp 1H NMR spectra are typical of isotropic fluids, whereas solid and liquid-crystalline materials give rise to much broader spectral lines. The results suggest the sharp 1H NMR spectra of human atheromatous lesions at body temperature are due largely to the presence of intracellular and extracellular droplets of cholesteryl esters in the isotropic liquid phase. These findings provide a necessary basis for use of 1H NMR techniques to image quantitatively the lipid constituents of human atheroma in vivo, and to study their chemical and physical properties.