Previous investigators have endeavored to discover any relation between manic or depressive states and function of the thyroid gland by determination of the basal metabolic rates of patients with such conditions.1 It is impossible to obtain reliable and accurate basal metabolic rates for overactive or apprehensive patients. For patients without psychosis, the concentration of iodine in the serum has proved to be an extremely accurate criterion of thyroid activity. In a study of several hundred subjects with and without thyroid disease, values for serum iodine below 3 micrograms per hundred cubic centimeters indicated hypofunction,2 and values above 9 micrograms per hundred cubic centimeters denoted overactivity of the thyroid gland. Conversely, serum iodine concentrations within the limits of 3 and 8 micrograms per hundred cubic centimeters were almost never observed for subjects with definite abnormality of thyroid function. Values between 8 and 9 micrograms per hundred cubic centimeters were