In studies of hydrolysis and synthesis of cholesterol esters by aortic enzymes, conventional methods (aside from isotope methodology) are too insensitive to measure reaction products when few aortas are used. High-performance thin-layer chromatography coupled with spectrodensitometry of plates charred after spraying with a cupric acetate-phosphoric acid reagent permitted quantitation of 10-ng amounts of cholesterol, cholesterol oleate oleate, and oleic acid. Linear calibration curves were obtained after spectrodensitometry of chromatograms containing 10-200 ng of lipid. The results were verified by radioassay.