The major lipid changes caused by adding 5% Wesson Oil and 1% cholesterol to cockerel diets were large increases in serum cholesterol, cholesteryl esters, and triglycerides. Lecithin and cephalin were not affected. Ascorbic acid significantly increased serum triglycerides; vitamin E significantly lowered serum cholesterol. Percentages of the saturated acids (palmitic, stearic, and arachidonic) of cockerels on the Wesson Oil-cholesterol diet decreased significantly; unsaturated linolenic and linolenic acids increased, and oleic acid remained the same. Dietary ascorbic acid seemed not to affect fatty acid distribution significantly, but when vitamin E was added to the diet, the stearic acid percentage rose and oleic acid percentage was lower. Acrylamide-gel electrophoresis showed that changes the vitamin E caused in the lipid and protein constituents of cockerel serum differed from changes the Wesson Oil-cholesterol diet caused.