were still below control levels, but by one year post-exposure they had returned to thelevel of the comparison population. Platelets fell to about 30% of the control values by the fourth week. By six months they had reached 70% of the controls; at one year the mean platelet count wasstill below that of the control population but slightly higher than atthe sixmonth survey. At two years the platelets, though still slightly below the control level, showed some further increase over the one-yearlevel. The depression of blood elements in the Ailingnae group whoreceived an estimated dose of 69 r was similar to that in the other group except that it was less marked. Even though thedoseofirradiation received by the Utirik people was quite low (about 14 r), a slight depression of platelets wasobserved duringthefirst month post-exposure. Changes in the hematocrit were not remarkable in any of these groups. Clinical observations revealed no disease processes or symptoms which could be attributed to radiation effects aside from skin lesions, loss of hair, and early symptoms. The diseases encountered were no moresevere or frequentin the irradiated than in the nonirradiated population even during the period of greatest depression of the peripheral blood elements. Up until the two-year examination no deaths had occurred amongtheirradiated people. It was difficult to evaluate the effects on fertility; however, a number of apparently normal babies were born and further pregnancies occurred. No opacities of the lens or other eye changes were found that could be attributed to irradiation. The height and weightof the irradiated children wereslightly less than those of the unirradiated children of the same age, but because of the small numbers of children involved, no definite statement could be made. Beta Irradiation of the Skin Noaccurate estimate of the radiation dose to the skin could be made. Lesions of the skin and epilation appeared about two weeks after exposure, largely on parts of the body not covered by clothing. Most of the lesions were superficial; they exhibited pigmentation and dry, scaly desquamation and wereassociated with little pain. Rapid healing and repigmentation followed. Some lesions were deeper, exhibited wet desquamation, and were more painful; a few became secondarily infected. Repigmentation gradually took place in most instances, and someofthe healing lesions, particularly on the back of the neck, developed hyperpigmentation of a grayish, dusky color and a thickeningof the skin with “orangepeel” appearance. At one year, however,this type of pigmentation was greatly reduced. Deeper lesions on the dorsum of the feet continued to show lack of repigmentation, with scarring in some cases. At two years post-exposure 15 cases continued to show residual skin effects largely in the form of pigment aberrations, and someatrophy and scarring. Histopathological studies of the skin showed changes consistent with radiation damage. A commonfindingin acute lesions was spotty transepidermal damage accompaniedby atrophy and flattening of the rete pegs with areas of relatively normal skin between. The dermis was muchless affected than the epidermis. Biopsies taken on later surveys showed considerable improvementbut with somepersisting changes.* In no case was there evidence of any premalignant or malignant change. Pigmentation of the semilunararea ofthefingernails and toenails was observed in about 90% of the people about three weeks after exposure. By six months pigmentation had largely grown out with the nail and had disappeared in mostcases. Internal Irradiation Radiochemical analysis of numerous urine samples of the exposed personnel showed some degree of internal absorption of radioactive materials, probably brought about through eating and drinking contaminated food and water. Calculations of the body burden of these materials, how- ever, showed that the concentration was too low to result in any serious effect. Analysis of urine samples six months after exposure showed only barely detectable radioactivity present in some cases. At two years radiochemical examination of pooled urine samples showed Sr°°=0.6 and Ce'**-Pr'+*=7.0 disintegrations per minute per 24-hr sample. (The samples were not analyzed *In some sections acanthosis, absence of pigment in the basal layer, and atrophy and benign dyskeratosis were noted tn the stratum spinosum of the epidermis. Changes noted occasionally in the dermis consisted of areas of homogenization and increased density of collagen, alteration in the distribution of mucopoly- saccharide, presence of mucin in areas of degeneration, and capillary dilatation.