43 population is difficult to explain. Evidence for residual bone marrow injury mavalso be associated with continued slight depression of the peripheral blood elements noted above, the finding of bizarre nuclear forms and binucleated forms in bone marrow examinations, anda slight increase in incidence of aneuploidy and 2-hit aberrations in chromosomestudies of cultures of the peripheral blood lymphocytes. to the dose of radiation received. Even in the 157 Utirik pepole who received only an estimated 14 rads, it was possible to distinguish slight plate- let depression in the group as a whole. The smaller groups on Ailingnae and Rongerik showed peripheral blood levels between those of the high and low exposure groups. The chronological records of blood findings in the group exposed on Rongelap are presented in Figures 38 to 41 and Appendix 8. Lymphopenia of about half the level of the Summaryof Findings in Rongelap People Over the Past 15 Years The effects of fallout radiation on the exposed Marshallese can be categorized as prodomal, acute, andlate effects. Some special studies are also dis- cussed below. PRODROMAL RADIATION EFFECTS During the first 24 to 48 hr after exposure, about % of the people experienced anorexia and nausea. A few vomited and had diarrhea, many also experienced itching and burning of the skin, and a few complainedoflacrimation and burning of the eyes. None of these symptoms was noted in the Utirik people (14-rad group). Following this, the people remained asymptomatic until about 2 weeksafter the accident when cutaneouslesions andloss of hair developed, due largely to betairradiation of the skin. It was apparent when the people werefirst examined, a few days after exposure, that the lymphocytes were considerably depressed and thatsignificant doses of radiation had probably been received. In addition to the whole-body dose of radiation and the beta irradiation of the skin, radiochemical!analyses of the urine showed that measurable amountsof radio- active material had also been absorbedinternally. ACUTE EFFECTS Penetrating Radiation Oneof the earliest findings indicative of a significant exposurein these people was lowering of levels of leukocytes and platelets of the peripheral blood. This was most marked in the 64 people on Rongelap whohad received 175 rads andless so in the other groups receiving less exposure. The hemopoietic depression was roughly proportional comparison Marshallese population was evident whenthe people exposed on Rongelap werefirst examined ontheir arrival at Kwajalein 3 days after exposure (see Figures 39 and 41). In children <5 years of age the lymphocytes dropped to 25% of the levels in the comparison children, but showed a slight rise during the following weeks. The lymphocyte level showeda slight increase by 1 year. In the following year mean counts ap- proachedthelevels of the comparison population but remainedslightly below it. Neutrophil ievels fluctuated considerably during the first month; possibly this was related to the prevalence of beta burns of the skin during that period. Neutrophil depression becameevident by 5 and 6 weeks post exposure (see Figures 38 and 41) with levels reaching about half that of the comparison population in the adults and slightly lowerin the children <5 years of age. This degree of neutropenia wasinsufficient to result in anv apparentincreased infectious processes, and, indeed, it was noted that neutrophilic leukocytosis waspossible in people showing casual infections at this time. Neutrophil levels recovered more rap- idly than lymphocyte levels and reached near control levels by 1 year. Subsequent annual survevs have revealed that recovery does not appear to have been complete, particularly in younger and older age groups, during the 15-year period. Early platelet counts showedless fluctuation than other blood counts andfairly consistently showed increasing depression, reaching levels of about 30% that of the comparison population bythe 4th week. A spurt of recovery to about 73% of comparison levels occurred during the following few weeks, which was followed by slower recovery but with mean levels never reaching higher than 90 to 95% that of the comparison population during the 15 years post exposure (see Figures +0 and 41). Erythropotetic depression has not been a consistent finding as with the leukocytes and thrombo-