1. Thyroidectomy in itself does not cause a rise in blood cholesterol or the development of atherosclerosis in young rabbits.
2. Feeding cholesterol produces hypercholesterolemia and atherosclerotic lesions in rabbits regardless of the presence or absence of the thyroid glands.
3. Potassium iodide prevents the usual hypercholesterolemia and atherosclerosis of the aorta in normal rabbits fed cholesterol, but when the thyroids are removed this protective action disappears.