The effects of the feeding of diets containing equal amounts of saturated fatty acid, oleic acid, and linoleic acid, respectively, upon the composition of the plasma cholesterol esters in human subjects were evaluated. Plasma cholesterol esters mirrored to a significant degree the kind of fat which was fed. The feeding of linoleic acid resulted in a very significant descrease in the level of plasma cholesterol in association with a high level of di-enoic acid in the cholesterol ester fatty acids. Feeding of a fat-free, high carbohyrate diet resulted in cholesterol ester fatty acid composition similar to that noted in patients receiving dietary oleic acid, but in a much higher total lipid. The oleic and linoleic acids were fed in the form of the ethyl esters.