The relationships between the serum cholesterol concentration, the basal metabolic rate and the clinical aspects of hypothyroidism induced by total removal of the normal thyroid gland in patients with chronic intractable heart disease have been studied and are reported in this communication. 1 By means of preoperative measurements and measurements at appropriate intervals after total thyroidectomy, it has been possible to observe the development of changes in the serum cholesterol values and the basal metabolic rate as hypothyroidism developed in these patients who before operation had no thyroid disease. The development of untoward symptoms of myxedema necessitated the administration of minimal amounts of thyroid substance to many of the patients, thus affording an opportunity to study the effect of this medication on the aforementioned relationships. Mason, Hunt and Hurxthal 2 reviewed the literature up to 1930 on the relationship of blood cholesterol concentration to the activity of the thyroid gland