Fat mixtures containing 10, 30, 60, and 70% saturated fatty acids as glycerides were fed to male rats at a level of 17% by weight of a chow diet. The saturated acids were mainly palmitic rather than lauric and myristic as previously used. In confirmation of earlier results the fat mixture containing 30% saturated fatty acids produced the greatest weight gains and the highest food efficiency. The same trend was noted when similar fat mixtures were added to a purified diet but differences in weight gain and food efficiency were not significant. The source of fatty acids had no effect on weight gains. The excretion of total lipids was not influenced by the degree of saturation of the fats within the limits studied. Shortening, however, caused increased excretion of total lipid. There were no significant differences in liver and adrenal weights produced by these diets.