The conversion of ethanolamine to phosphatidyl choline was studied in liver slices from rats exposed to a high dietary intake of cholesterol in the presence of cholic acid. Cholesterol stimulated phosphatidyl choline formation per unit weight of liver tissue and increased the total liver mass thereby increasing further the total yield of phosphatidyl choline. These results are contrasted with the opposite effect of cholesterol on the liver phosphatides of the rabbit. A relationship between phosphatides and cholesterol metabolism and between species susceptibility to cholesterol induced atherosclerosis and phosphatide metabolism is pointed out.