74 myelogenous form, since his past hemograms showed fairly consistent depression of neutrophil counts compared with those of other exposed boys of the same age. Theinability to demonstrate clear-cut agingeffects in the exposed groupin spite of repeated at- tempts with a variety of tests is in accord with the generally negative results of similar attempts in the much larger exposed Japanese populations. The absence of radiation-induced cataracts is not unexpected since the dose to the lens was probably below threshold and neutrons (known to have a higher RBE for cataract induction than gammaradiation) were not involved in the Mar- shallese exposure. E. THYROID EFFECTS The high incidence of thyroid neopiasms(in 27 of 86 exposed Rongelap people, including 3 with carcinomas) and the developmentin somechildren of hypothyroidism and growth retardation provideclear evidence for the seriousness of thyroid injury dueto radioiodine absorbed from fallout associated with atomic detonations. Had notcareful medical studies in the population beeninstituted soon after the exposure and continued tothe pres- ent date, the extent of thyroid effects might not have been discovered. Thyroid exposureis likely to be greater when individuals are exposed within 100 to 150 miles of the bombif detonated near the ground. In such situations,if lethal exposure to penetrating radia- to the higher dose to the child’s thyroid because of its smaller size. The rapid growth of the glands during childhood probably increased the chances for neoplastic changes. The growth retardation in someof these children was thoughtto be related to reduced thyroid function resulting in lower hor- monelevels. This deficiency was not recognized during the early years becauseoffalsely high PBI levels resulting from unusually high iodoprotein levels, which turned out to occur generaily in the Marshallese and are now being further studied. Most ofthe thyroid glands of the exposed people undergoing surgery contained multiple nodules or areas of adenomatous change. Many microscopic areas, although considered benign, were composed of discrete areas of atypical ceils, suggestive in some cases of malignant potential. Therisk of developing benign and malignant neoplasms in the Rongelap people appeared to be about the sameas that noted in people exposed to x-radiation. Clinical experience with 111 suggested that the risk would have beenless,-but the higher energy of the short-lived isotopes of iodine (particularly 132], 133], and 1351), resulting in higher dose rate and more uniform exposure of the thyroid, is thought to have been the important factor in increasing the numberof thyroid abnormalities above that expected from similar doses from 131] alone.It is not unreasonable to speculate that tumorincidence in the Marshallese would have been considerably smaller if only !°11 had been involved in the exposure. The lesser amount of short-lived iodine isotopes in the Utirik expo- tion does not occur, the principal hazard appears sures (because of the later arrival of the fallout) leukemia. Since thelatter is ultimately fatal,it is more serious than thyroid malignancies, most of which are weil differentiated and have an excel- sion to be drawn. to be the late developmentof thyroid tumors and lent prognosis. The relative incidence of thyroid malignancies from radiation appears to be about the same as that of leukemia on a “per rad”basis.177 Theincidence of thyroid canceris considerably higher than the mortality from it. Of 40 cases among the exposed Japanese, 34 wereliving in 1973, and only one death had beenattributed to this cause. No evidence of thyroid dysfunction had been noted at the time of diagnosis. In the Marshallese reduced function was not foundin twoof the cancer cases exposed as adults, but was in the case exposed as a child. The high incidence of thyroid effects in children exposed at < 10 years of age was no doubtrelated 900o1 TI may have been an importantfactor in reducing the dose effect to their thyroids, but the numberof people involved is too small for any firm concluTreatment of the exposed Rongelap people with thyroid hormonehas been of benefit in enhancing growth and developmentin the growth-retarded children and in maintaining a normal metabolic state in the operated cases. It is not certain whether it has prevented the development of thyroid nodules. The documentation of these thyroid effects has importance not only for the people involved but also for the advancementof medical knowledge and for planning with regard to Civil Defense and remotely possible future accidents involving re- lease of radioiodines(e.g., from a nuclear power plant). The Marshallese accident represents ex-