TABLE OF CONTENTS Introduction. Previous studies of the respiratory exchanges. Methods of experiment. Case histories. Discussion of Results: The basal metabolism in exophthalmic goiter. The respiratory quotients. Direct and indirect calorimetry. The water elimination through skin and lungs. Specific dynamic action of protein and dextrose. The effects of treatment. Observations on a cretin. Therapeutic applications. Summary and conclusions. To those who are accustomed to think in terms of the energy requirement, exophthalmic goiter stands outpar excellenceas the disease of increased metabolism, and the increased metabolism stands out as the chief symptom of hyperthyroidism. The determination of the heat production seems to afford the best index of the severity and course of the disease. There is great need of some purely objective test in hyperthyroidism to indicate the effect of treatment, since psychotherapy