The effect of hypothyroidism on the specific dynamic action of carbohydrate and of protein in man and in animals has been previously studied by several investigators. The results of these studies and their interpretations vary. In a group of patients at this hospital hypothyroidism has been induced by total ablation of the normal thyroid gland for the treatment of chronic heart disease (1)(2). An opportunity was thereby presented to reinvestigate the effect of hypothyroidism upon the specific dynamic ac-tion in man. Total thyroidectomy was performed in these patients in order that in the hypothyroid state they might derive the benefits of the lessened demands upon the heart (2)(3)(4). It seemed important to establish whether or not these in-dividuals, in addition, were relieved of the increased demands upon the circulatory system co-incident to increased metabolism after the inges-tion of food.