1. Whole thyroid gland when administered simultaneously with cholesterol prevented the atheromatous changes produced by the latter in the aorta of rabbits in 17 of 19 animals.
2. In this series thyroxin was less effective, as atherosclerosis occurred in 8 of 11 rabbits.
3. Potassium iodide also exerted a strong protective action as aortic lesions were present in only 1 of a series of 12 rabbits fed cholesterol and potassium iodide concurrently.
4. The effectiveness of potassium iodide was not shared by potassium bromide or potassium chloride.
5. A relationship was noted between the level of the cholesterol in the blood and the development of atherosclerosis. In general, the aortic lesions accompanied a hypercholesterolemia.