S TUDIES mnade at this university on the effect of different kinds and levels of fats on the excretion of urinary metabolites of rats and later of man focused our interest on what was happening to the serum and liver cholesterol values of the subjects. Of the nutritional factors which may affect the level of cholesterol in blood, the kind and level of dietary fat has been under intensive study in a number of laboratories. Recent studies involving fats alone or in combination with other factors have been reported. Okey and Lyman’ found that serum cholesterol values of rats fed 10 jer cent coconut oil tended to be higher than those of rats fed partly hardened cottonseed oil. Liver cholesterol storage was greatest on the cottonseed oil diets. When Aftergood et al.2 used 15 per cent lard and 15 per cent cottonseed oil, they found that feeding the lard diets resulted in higher liver and serum cholesterol values when the diet contained cholesterol.