and progressively decreased, attaining a minimum between the 25th and 30th day. Al~ though recovery commenced following this minimum, the platelet count had not returned to normal by completion of the initial study on the 76th day after exposure. The incidence of various respiratory and skin (cutaneous) infections was identical in all exposed g: oups and had no relationship to the hematologic changes. Urinary excretions of radio-isotopes were studied. Beta activity in the urine of these exposed human beings indicated significant internal contamination. The body burden of the group of human beings with the greatest contamination was of the order of the maximum permissible concentrations for the individual radionuclides. The contribution of the effects of internal contamination to the total radiation response observed appears to have been small. Few of the fission products present in the environment were readily absorbed by the blood stream from the lungs and the ,astrointestinal tract. Most of those radio-elements that gained entry into the body had short radiological and biological lives, and thus, the level of activity in the tissues of the body was relatively low. At the end of six months, follow-up medical examinations were made of the Marshallese inhabitants of Rongelap. In general, the individuals appeared healthy and normally active, and no deaths had occurred in the interim period. Three babies had been born since exposure, none of whom displayed detectable abnormalities. One miscarriage at 3 months occurred during the interim period; no specimen was available for study. The skin lesions previously prominent had healed completely, and only occasional hyper- pigmentation of depigmented scars was seen in a few individuals who had severe early skin damage. Regrowth of hair had commenced during the third month following exposure and was essentially complete at the six-mcnth examination. Residual discoloration of the fingernails was found in three individuals. No additional physical-examination findings could be ascribed to radiation exposure, and most individuals had gained weight during the interim period. An epidemic of mea- sles was in progress during the examinations. The severity of the disease in the Rongelap people wes no greater than in a control, unexposed population, and the incidence was no higher. Chest X-rays of all individuals revealed no abnormalities ascribable to the fallout radiation. Analysis of hematological data obtained failed to demonstrate a significant effect of measles on the peripheral blood count. Neutrophile, lymphocyte, and platelet counts were not significantly different from counts taken on the 74th post-exposure day, and none of these values had returned to control levels. Studies of bone marrow specimens obtained on 20 adult individuals revealed no significant abnormalities. Mini- mal amounts of residual radioactivity were detectable in the urine of approximately one third of the exposed individuais. 72