particularly with regard to the thyroid. More information would be desirable concerning certain aspects of thyroid exposure. More data are needed on the contribution of short-lived iodine radioisotopes, including relative abundance and distribution as a function of time, dose fractionation, etc. Also, the dose-response relationship of these isotopes in the thyroid compared with ly and gamma radiation needs further investigation; such studies should be done in large animals, perhaps sheep or swine, having thyroid glands comparable in size to human glands. Since radioelements other than iodine may have been involved in the thy- roid exposure of the Marshallese, further information is needed on such elements that might be present in fallout. Certain elements are known to show relatively greater affinity for deposition in the thyroid than in other organs. Radium and thorium (226,227), barium (226), americium (228,229), plutonium (228-230), and calcium (226,231,232) have been found in animal thyroid glands. Robison et al. (231) have shown that calcium is concentrated in the lining of thyroid follicles with small localized areas of calcification in human thyroid glands. Haeberli et al. of 45ca in the rat thyroid. (232) have reported rapid incorporation In view of the abundance of calcium in the atoll environment, perhaps consideration should be given to the possibility of a neu- tron-induced calcium isotope that might have been involved in the thyroid expo~ sure of the Marshallese. Autoradiographic and other studies of animal thyroids removed at surgery or autopsy might be helpful in this regard. It should be noted that the elements referred to above are absorbed by the thyroid to a much smaller degree than iodine, and it seems unlikely that they would contribute significantly to the thyroid dose. Very little is known about the effects of low doses of radioiodine radia- tion on the thyroid. One source of information comprises thyroid studies on people given diagnostic doses of 13ly in the early days, when doses were higher than now used. It is hoped that further information from such studies will be forthcoming so that a better evaluation can be made of low-dose ef- fects and of the relative importance of 131] exposure on the thyroid. The development of thyroid nodules in two of three Rongelap children exposed in utero emphasizes the probable importance of radioiodine absorption by the fetus from the mother. More precise information regarding fetal iodine uptake at various stages of gestation is needed. 1297, a long-lived isotope with low radioactivity and a high cross section for neutron activation, might be administered to pregnant women in cases where abortion is indicated. Neutron activation of !29f in the thyroid gland removed from the fetus would provide precise information on uptake of iodine by the gland at the given stage of gestation. In view of the greater relative sensitivity of the child's thyroid, fur- ther information on thyroid weights and thyroid function in children of vari- ous ages would be helpful. In conclusion, in view of the possible further development of thyroid abnormalities and other late effects of radiation in the exposed Marshallese people, it is necessary that regular examinations and provision for adequate health care be continued throughout their lifetime. - 88 -