ABSTRACT Follow-up medical examinations were made of the Marshallese inhabitants of Rongelap Atoll 6 months after they had been exposed to atomic bomb fallout radiation during the Operaiiua CASTLE test series in March, 1954. During the early atute period following exposure, these people had shown systemic effects and marked hematological changes resulting from penetrating gamma radiation; extensive superficial skin lesions and epilation associated prin- cipally with beta and soft gamma radiation from fallout material deposited on uncovered skin areas; and minimal internal contamination with fission products, resulting principally from ingestion of fallout material. At the time of the 6-month resurvey the individuals, in general, aioe appeared healthy and normally active, and no deaths had occurredin 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 spc.imen was available for study. The skin lesiors previously prominent had healed completely, and only occasional hyperpigmentation 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 6-month examination. Residual of the fingernail discoloration previously noted was found in three individuals. No additional findings on physical examination could be ascribed to radiation exposure, and most had gained weight during the interim period. A measles epidemic was in progress during the examinations. The severity of the disease in the Rongelap people was 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 individuale revealed no significant abnormalities. Minimal amounts of residual radioactivity were detectable in the urine of approximately one-third of the exposed individuals. WSREE