FALLOUT EFFECTS—MARSHALL ISLANDERS 67 animals. The lack of carcinoma in the high-exposure group might therefore be due to an overkill effect. Thelatent period before detection of hypofunction in the more highly exposed Rongelap children was shorter, and the hypofunction was more pronounced, than in the people receiving less exposure. Earlier cell death at mitosis in their growing thyroids and increased interphase death with these higher doses may have accounted for this. The later appearance of decreased thyroid function in the lower-dose adult group suggests that the delay was related to slower turnover of cells in the adult gland and probably to reduced interphase death at lower doses. Earlier appearance of nodularity in the younger age group would seem logically to be associated with earlier increased stimulation from TSH associated with the earlier hypofunction. DISCUSSION The fallout accident involving the Marshall Islanders did not result in early. mortality and, except for a case of leukemia and possibly one other cancer, late effects thus far have been predominantly thyroid abnormalities from exposure to internally absorbed radioiodines and gammaradiation. Thyroid effects of the Marshall Islands accident are not strictly comparable with such effects that might occur from accidents involving nuclear power sources. Analysis of the Three Mile Island accident (63) has indicated that the amount of radioiodines released into the atmosphere was substantially less than that predicted in the Reactor Safety Study [the so-called Rasmussen Report (57)]. This should be kept in mind when comparing potential casualties from nuclear warfare versus reactor accidents. In the event of nuclear warfare the total exposures from released radionuclides could be muchlarger than they were in the Marshall Islands accident. In such situations the effects of gammaradiation would likely predominate with regard to both early and late effects of exposure. Malignancies that might develop as a result of such exposure are morelikely to be fatal than thyroid malignancies, which are more amenable to medical and surgical treatment. From the Marshallese experience it is clear that, in any future accident involving radioiodines, the use of oral stable iodine to suppress radioiodine uptake by the thyroid, particularly in children and pregnant women, should be considered (9,46). People who have been exposed to significantfallout should have regular examinations, including testing of their thyroid status with sensitive tests of thyroid function now available. Even though the prophylactic value of thyroid hormone treatment in preventing development of thyroid abnormalities has not been proved in the Marshallese or other humans, such treatment is sound and should be considered. From the Marshallese experience it is apparent that more information is needed in several areas regarding their exposure.