Many aspects of the pathogenesis of coronary artery disease remain to be clarified, and particular interest centers on the metabolism of fats. The author has studied the reactions of patients to different diets by standard chemical studies of total lipids, phospholipids, and cholesterol in the blood and also by a study of the particle-size of the liproproteins of the blood. The results led to the conviction that the diet of patients with coronary artery disease should be designed to maintain the total blood lipid levels as well as the various fractions within normal limits. This is accomplished by limiting the daily intake of total fat to 50 Gm. and keeping the intake of saturated fats as low as possible.