changes might have appeared in the thyroid if these patients had survived. However, the evidence from other studies atrongly indicate that ‘if any pathological effects were to be noted in the thyroid after an exposufte of some 10,000 reps they would be minimal. Likewise, the possibility of serious damage to other organs of the body, such as parathyroids and. trachea which are simultaneously exposed to the zi31 radiations, would be exceedingly amall. On long term effects, two summrizing statements may be made. "No thyroid neoplasm was found which could be attributed to 3din 26 after doses to normal thyroids running into many tens of thousands of reps and after periods of observation up to more then eight hundred days. “In a series of over }00 patients treated with radioactive iodine at the Maseschusetts General Hospital during the past ten yeare no kmown carcinoma of the thyroid attributable to this agent has developed. Definite answers to the question of carcinom formation mst await prolonged observation of treated patients.” 23 Here the average treatment dose of pt was 10 millicuries and of 330 25 millicuries. However, significantly lesser doses may be carcinogenic in children.”! "---It has been suggested that the human thyroid is less radiosensitive than other tissues, such as bone, since after many years of treatment of Graves’ disease with redioactive iodine, no cases of resulting carcinom bave bean reported. The customary dosages of 731 in such cases yield at lenst 4000 rep to the gland. On the other hand, carcinom of the thyroid found in children and young adults bas almost inveriably been preceded by x-ray treatmant to the upper part of the bocy, in amomts such es to yield ag little esx 200 r to the irfant thyroid. It has been estimated that less than 3% of such DOE ARCHIVES G(