A reported elevated basal metabolic rate (BMR) must-not be accepted as certain proof of the presence of thyroid hyperactivity since many other factors exert an influence on metabolic rate. Metabolic tests were taken under pentothal anesthesia in an attempt to secure a truly basal state. In normal patients the metabolic rate dropped an avg. of 13% under pentothal anesthesia and an avg. of 1 g. of pentothal was necessary to induce anesthesia. Patients with hyperthyroidism showed little drop in BMR under anesthesia and 2 g. or more of pentothal was required to produce sleep. Patients with greatly elevated metabolic rates due to various nervous states had a drop in BMR to normal under anesthesia, indicating an absence of hyperthyroidism. This method of metabolism testing induces a perfect basal state[long dash]the resulting rate being void of all nervous and muscular factors. In the occasional problem patient with an elevated metabolic rate this procedure may be used to good advantage; such cases are reported. The test has been used to advantage in determining the safest time for operation on patients with hyperthyroidism who have associated nervous states and in whom satisfactory metabolism tests are difficult to obtain. Hypertensive patients with elevated rates had a lowering of the metabolic rate under anesthesia, showing that the occasional increased rate of the hypertensive patient is related to a tension state and not to the hypertension.