21 norma] and that from 16 to 64% of the natives on Rongelap and 90% on Utirik showed values that were above the normal range by American stan- dards.?* No significantdifferences in the PBI levels were noted between the group that had beenex- posed to radiation and the unexposed group. Chemical studies ofthe sera revealed that the high girl (217), and the following year a 13-vear-old (2221) and a 14-yr-old girl ( +69), both exposed, were also found to have nodules of the gland.23 Since then increasing numbers of thyroid abnor- malities have appeared in the exposed Rongelap people. In 19 people nodularity of the gland has been the prominent finding, and in 2 boys (3 and 5) atrophy of the gland has developed. The nodules were usually multiple and non-tender and varied in consistency. Surgical exploration, de- PBI levels could be accounted for largely on the basis of high iodoprotein levels. Lack of recognition of this fact may have masked an incipient deficiency of the thvroid hormonein somecases dur- scribed below, has been carried out in 18 of the 19 Morerecently, after developmentof thyroid ab- lesions were foundin all these cases, and malignant ing these earlv studies. normalities in the exposed Marshallese, it was possible to compare serum iodoprotein levels in cases with thyroid hypofunction with those in euthyroid populations. In Table 12 iodoprotein levels are compared for the Ailingnae, Utirik, Rongelap unexposed, and Rongelap higher exposure groups with and without thyroid abnormaiities. The highest iodoprotein values were noted in the Utirik population. The Rongelap unexposed population had higher values than the exposed population. The reasonsfor this are not apparent. Amongthe exposed population those with thyroid abnormalities showed about the same mean level as those with.no thyroid abnormalities. Following thyroidectomythe iodoprotein levels were slightly lower, but no difference was seen between those with subtotal and those with total thyroidectomy. These data indicate that radiation exposure may have resulted in a slight reduction of iodoprotein levels in the exposed population. Thyroidectomy, partial or complete, resulted in only a partial reduction in the iodoprotein levels; therefore, it appears that the major portion of iodoproteins are producedat extra-thyroidalsites. Urine iodine levels were in the normal range in the Rongelap people, which indicates adequate intake in the diet, but the values were not quite as high as expected in individuals living close to the sea and eating seafood. 132] uptake studies showed a depressed thyroidal iodine uptake rate and renal excretion rate in the Marshallese (unexposed people) compared with Americans. No explanation for these findings is available. These data are described in detail in the preceding report.!! Developmentof Thyroid Lesions Nine years after the accident an asymptomatic thyroid nodule was detected during routine annual physical examination in a 12-year-old exposed nodular thyroid glands. Benign adenomatous lesions were also present in 3 of them. Oneadult with somewhat less significant nodularity of the thyroidis still under observation. Table 13 outlines the findings on individual cases. Appendix lists thyroid information on the entire exposed Rongelap population (including PBI, cholesterol, etc.). In view of the seriousness of these thyroid develop- ments a panel of experts advised that the more heavily exposed Rongelap people be given supplemental thyroid hormone. This treatment wasin- instituted in September 1965. Table 14 lists the incidence of benign nodules (including atrophyof the gland) and malignant lesions and the estimated dose of radiation to the thyroid glands in the various populations under study. The highest incidence of thyroid lesions (89.5%) has been noted in the heavily exposed Roneglap group who were <10 years of age at the time of the accident. The absenceof lesions in people of the sameagein the lesser exposed and unexposed groups is most notable. The incidence of thyroid lesions in those exposed as adults in the more heavily exposed group is considerably lower than in those exposed as children but is higher than in the adult population of the Utirik or unexposed groups. (One individual was found to have an adenomatousthyroid lesion in the Ailingnae group.) The first case of carcinoma of the thyroid was discovered in 1965 in a 41-vear-old woman (= 64) in the heavily exposed group, 11 years after exposure.?4-25 At that time the relationship of radiation exposure to appearance of this lesion was seriously questioned, although suchlesions are rare in the Marshallese. However, in September 1969 surgical exploration of the thyroid on 5 Marshallese with palpable nodules revealed malignantlesions in 3 additional people. Two of these were women in the more heavily exposed Rongelap group, a 36-