THIS PAPER deals with the spontaneously atherosclerotic White Carneau pigeon, and the atherosclerosis-resistant Show Racer pigeon; other breeds also have the disease, but will not be discussed. The White Carneaux come from a strain inbred since 1916. The morphologic, biochemical, and genetic aspects of the disease will be outlined. The effect of certain diets and therapeutic agents on the disease will be mentioned. The original groups of birds used in this study, both Show Racer and White Carneau, had been kept under identical conditions of diet, bousing, and exercise. Their diet is a mixture of corn, peas, wheat, and milo, with a mineral supplement and water ad lib. They were housed in large open-front lofts with a wire-enclosed fly pen permitting restricted exercise. The pigeons were from 4 to 8 years old. Subsequent studies have dealt with birds both older and younger than this original group. In the White Carneau