The United States Atomic Energy Commission first released radioiodine (I131) for general use in July, 1946. This material was made in the atomic pile at Oak Ridge. Investigations with the isotope were then initiated to determine the clinical value of the isotope in the diagnosis and treatment of hyperthyroidism, in addition to the studies in many other fields. Prior to this, radioiodine had been tried in the treatment of hyperthyroidism. Hertz and Roberts1and later Chapman and Maloof2had available to them I130, the 12-hour half-life isotope of stable iodine, made in the cyclotron. Hamilton and Lawrence3employed I131, the 8-day half-life isotope. Except for the few patients treated by Soley with these latter investigators, I131was not used further until the action of the Atomic Energy Commission; and at that time therapeutic interest in I130virtually ceased. The highly successful initial