In view of the importance of the late development of thyroid abnormalities, the estimates of dose to the thyroid gland are presented in some detail here. The dose from radioactive iodine is determined by its uptake by the gland, its half-life in the gland, the size of the gland, and the relative proportion of the several radioisotopes of iodine involved. The relative distributions of the radioiodines in fallout is reasonably well known. the isotopes 133;, to the thyroid dose. [In addition to 131; 1357, and to a less extent 132, contributed significantly The only direct data available on the Rongelap people are radiochemical analyses of pooled urine samples taken 15 days and longer after the fallout. The l day thyroid content of 1311 was estimated to be 11.2 mCi (5.6 to 22.4 mCi). Assuming that 0.1% (0.05 to 0.2%) of the maximum thyroid burden(not corrected for physical decay) was excreted in the urine on the 15th day(Ng), James has calculated a dose of 160 rad to the adult thyroid from oral intake and inhalation of the various iodine isotopes, considering their fission yield, the average energy deposited in the thyroid gland per disintegration, and the time of absorption. The dose to the thyroid glands of children less than 4 years of age was then calculated by means of these factors with consideration of pulmonary function and the thyroid size of a child of that age. The small size of the childhood thyroid then resulted in a substantially larger dose. The total estimated mean dose from the various iodine isotopes to the childs gland was about 1000 rad, with a range of 700 to 1400 rads. The glands received an additional 175 rads from external gamma radiation. Although the skin overlying the thyroid gland was frequently the site of "beta burns" as shown in Fiyure 6, the deposit of radioactive materials in this area probably did not add significantly to the thyroid dose, since most of the beta irradiations were too weak to have penetrated 50071309