46 came apparentin 2 boys exposed at 15 monthsof age who showed the greatest growth retardation. High TSH levels indicated a primary injury of the thyroid. Thyroid function tests on several other children with growth retardation showed evidence of thyroid deficiency (see below). Preliminary results of thyroid hormone therapy have indicated an improvementin growth in someof the children. Thyroid Findings By far the most significant of the late effects of fallout exposure noted in these people is a high in- cidence of thyroid abnormalities. Until the recent development of these abnormalities in 1965, the people were considered to be euthyroid and no ab- normalities of that gland were noted. The Marshallese people were found generally to have high serum PBI levels and unusually high iodoprotein values. The latter finding may have masked ear- lier mild thyroid deficiency. Dietary and urinary iodine levels had been in the normal range. Serum cholesterol levels were not indicative of thyroid disease. Thyroid uptake studies were generally normal but with some pecularities. In 1963 a thyroid nodule wasfirst detected in a 12-year-old girl, and since then increasing numbers of thyroid abnormalities have been noted. Between 1963 and 1966, 18 cases were detected, 15 in children ex- posed at <10 years of age and 3 in adults. Of these, 16 involved nodular giands, one of which was cancerous, and 2 involved complete atrophy (the growth-retarded boys mentioned above). No such abnormalities were found in the unexposed Rongelap children or theslightly exposed Utirik children, and only a low percentage of nodules was foundin the older unexposed population. The exposed population was placed on thyroid hormonetreatment in 1965. During the past 3 years further cases have developed; at present among the 66 exposed Rongelap and Ailingnae people now living (of the original 82) 3 have developed malignantlesions of the thyroid, 16 have developed benign nodules of the thyroid, and 2 have atrophy of the gland with hypothyroidism. These findings indicate the seriousness of the exposure to radioiodinesin fallout. The majority of thyroid lesions have occurred in persons who were < 10 years of age when exposed (90% of that group). Thyroidectomy, partial to complete, has been carried out on 18 Marshallese persons,thefirst 3 in Guam andtheothers in the United States following complete study at BNL. Theresults of these studies and the pathological findings, gross and microscopic, have been published in detail. The slight retardation of growth insome of the exposed children has been correlated with demonstrable deficiency of the thyroid hormoneassociated with radiation-inducedlesions of the gland. The supplemental thyroid hormone treatment seemsto be promoting skeletal growth in some of these children. A review ofthecase histories indicated a possible influence of puberty and pregnancy on the developmentof the thyroid lesions. The calculated risk of malignant lesions of the thyroid in the ex- posed Marshallese varied between 3 and 10 cases per 108 persons per rad per vearfor the different age groups. On the basis of these few cases, the risk of thyroid cancer from radioiodine exposure does not appearto be very different from that reported in persons following x-irradiation of the neck region in childhood. Eye Findings Ophthalmological surveys showed no remark-: able differences between the exposed and unexposed groups except possibly for a slightly greater incidence of pterygia, pingueculae, and corneal scars and pigmentationsin the exposed group. It is not known whetherthese findings are of anysignificance in relation to radiation exposure. As a whole, visual and accommodation levels in the Marshallese appear to be above the average in the U.S. population. In 1967 slit-lamp examinations of the lens showeda greater incidence of polychromatic sheen andlenticular opacities in the exposed than in the nonexposed population. Thedifferences were not thoughtto be significant, particularly in view of the higher meanageof the exposed group. In 1969 minute flecks of the optic lens were enumerated in the Marshallese. (In mice low doses of ionizing radiation cause the numberofflecksto in- crease significantly above that expected on the basis of age alone.) In both exposed and nonexposed Marshallese the numberofflecks increased with increasing age. The exposed females who were adolescent at the time of exposure had considerably higher fleck counts than comparably aged unexposed females. Preadolescent exposed males had fleck counts twice those in nonexposed males. The presence of these flecks was not thought to imply any likelihood of reduction in visual function. It was suggested that variation in sex hormones mightplay a role in radiosensitivity of the lens.