This is a report of a study in progress on thyroid function in patients with mental disease, and in controls, as measured by the uptake of the radioactive isotope of iodine, I131 by the thyroid gland, and compared with serum protein-bound iodine, basal metabolic rate, and plasma cholesterol. These 4 tests represent a combination of the best and most widely accepted methods for evaluating thyroid status known today.Data are given on 36 subjects: 24 patients and 12 controls, and includes a total of 61 basal metabolic rates, 66 plasma cholesterols, 65 serum protein-bound iodines, and 78 I131 uptake determinations. The largest diagnostic category studied is schizophrenia. The number of patients in all other categories is insufficient to establish any trends.The average basal metabolic rates are somewhat low in our subjects, the average plasma cholesterols somewhat high. The serum protein-bound iodines fall compactly within the normal range. The uptake of I131 is widely distributed, with uptakes below 10% and above 40% in several cases but, with the exception of one patient with an uptake of 60%, they fall for the most part within the normal range. In no case did the uptake curves on our subjects resemble the types found in myxedema or thyrotoxicosis. Most important, so far no significant difference has been found between patients and controls by clinical evaluation and as measured by both old indirect and new direct tests of thyroid function.Our results contrast with many reports in the past of low basal metabolic rate compared with normal controls, and of low plasma cholesterol in schizophrenic patients. Perhaps our more nearly normal findings are due to selection of a group for study with short duration of illness and short length of hospitalization. The significance of reports in the past on patients chronically ill and hospitalized for prolonged periods is open to question. On the other hand, the number of subjects we have studied, particularly control subjects, is still small, and it may or may not be that when a larger sample has been accumulated there will be a shift in trends.We find no change in thyroid function as measured by the above tests in patients during or after insulin shock, electroshock, combined shock, or psychotherapy. Thyroid medication, however, produced profound alterations in findings on all 4 tests in the 2 patients on whom study has been completed.It should be pointed out that there has been insufficient analysis of rate of I131 uptake; we have dealt in this paper primarily with the maximum concentration of I131 accumulated in the thyroid gland after a test dose. Since the data presented in this paper were analyzed, results possibly suggestive of some abnormality have been found on 2 depressed manic-depressive patients. (Both patients had a marked drop in their radioactive iodine uptake curve as they improved during electroshock therapy. One patient had an abnormally high initial uptake, the other a high normal uptake. The rate of uptake in the patient with the high normal curve was markedly delayed.) Studies of this diagnostic category, of anorexia nervosa, and of psychoneurosis, of analysis of varying rates of I131 uptake, and effects of thyroid medication are being pursued further, and will be reported at a later date.