Radiation therapy has an important and accepted role in the treatment of the various forms of hyperthyroidism. Many thousands of patients with Graves' disease have received roentgen or radium therapy with noteworthy success, particularly in properly selected cases. Hypothyroidism as a direct, immediate sequela of radiation to the thyroid for hyperfunction occurs only rarely. Case Report B. L., a white male 50 years of age, presented himself on Jan. 4, 1940, complaining chiefly of choking spells, nervousness, and loss of weight. His past history was negative except for a tonsillectomy a year and a half earlier performed under local anesthesia, and the presence of bilateral herniae held in place by a truss. Otherwise he had always been well. His father died of diabetes at forty-one years; his mother died of gallstones and heart disease at seventy-six years. Otherwise the family history was irrelevant. Two months before he was first seen the patient had become increasingly irritable and nervous and had observed a marked increase in perspiration. In the past month he had experienced numbness of the feet and cramps in the legs. For the last week, the onset of the irritable spells had been accompanied by severe choking sensations, lasting one to twominutes. There had been a loss of 15 pounds in two months. The patient did not appear acutely ill, but was very nervous and jittery. His weight was 181 pounds; blood pressure 140/80 mm. Hg; pulse 118 beats per minute. The pupils were equal and dilated, reacting slightly to light and in accommodation. Moderate exophthalmos was present. No other ocular abnormalities were observed. Nose, ears, and throat were normal. In the neck a uniformly enlarged thyroid was palpated. The cardiac apex impulse was felt in the fifth left interspace, 12 cm. from the mid-line. The heart rate was rapid. There were no shocks, thrills, or murmurs. No masses or organs were palpated in the abdomen, but bilateral indirect inguinal herniae were present. Rectal examination revealed no abnormalities; the prostate was not enlarged. Knee jerks and bicipital reflexes were increased, but there were no abnormal reflexes. Moderately severe fine tremors of the hands were present. Laboratory examination revealed no abnormalities in the urine. The Kline test was negative. The basal metabolic rate, determined on Feb. 1, was found to be plus 46. Radiographic examination of the neck and chest revealed a slight enlargement of the left ventricle. There was moderate displacement of the trachea to the right at the thoracic inlet,. indicative of an enlarged left lobe of the thyroid. Definite tracheal narrowing was absent. Thyroidectomy was refused. The patient was given 5 minims of Lugol's solution and 0.5 grain of phenobarbital with vitamin B three times a day. After two months of this therapy, the basal metabolic rate dropped from plus 46 to plus 24.