phocytes were considerably depressed and that significant doses of radiation had probably beenreceived. In addition to the whole-body dose of radiation and the beta irradiation of the skin, radio- chemical analyses of the urine showed that measurable amountsof radioactive material had also been absorbedinternally. The effects of the radiation can best be summarized underthree headings according to the modeof exposure: penetrating irradiation, skin irradiation, and internal irradiation. PENETRATING RADIATION One ofthe earliest findings indicative ofa significant exposure in these people was lowering of levels of /eukocytes and platelets of the peripheral blood. This was most marked in the 64 people on Rongelap who had received 175 rads, and was less marked in the other groupsreceiving less exposure. The hemopoietic depression was roughly proportional! to the dose of radiation received. Even in the 157 Utirik people who received only an estimated 14 rads, it was possible to distinguish slight platelet depression in the group as a whole. The smaller group on Ailingnae and Rongerik showed peripheral blood levels between those of the high and low exposu'e groups. The chronological! records of blood f ndings on the group exposed on Rongelap are pre:ented in Figures 49, 50, 56, and 63 and Appendix ¢, and on the Ailingnae and Uumk groups in Appendices 9 ard 10. Lymphopenca of about half the level of the comparison Marshallese population was evident when the people exposed on Rongelap-werefirst examined on their arrival at Kwajalein 3 days after exposure (see Figures 49, 50, and 65). In children <4 vears 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 showed a slight increase by | year. In the following year mean counts approachedthe levels of the comparison population but remained slightly below (see Figures 50 and 65). Neutrophil levels fluctuated considerably during the first month; possibly this was related to the prevalence of beta burns of the skin during that period. Neutrophil depression became evident by 2» and 6 weeks post exposure (see Figures 49 and 65), with levels reaching about half that of the comparison population in the adults andslightly lower in the children <5 ycars of age. This degree of neutropenia wasinsufficient to result in any apparent increased infectious processes, and, indeed, it was noted that neutrophilic leukocytosis was possible in people showingcasual infections at this time. Neutrophil levels recovered more rapidly than lymphocyte levels 2nd reached near control levels by 1 year. Subsequent annual surveys haverevealed that recovery does not appear to have been complete, particularly in younger and older age groups, during the 10-year period. Early platelet counts showed less fluctuation than other blood counts andfairly consistently showed increasing depression, reachinglevels of about 30% that of the comparison population by the 4th week. A spurt of recovery to about 75% of comparison levels occurred during the following few weeks, which was followed by slower recovery but with mean levels never reaching higher “han 90 to 95% that of the comparison population during the 10 years post exposure (see Figures 56 and 65). Erythropoetic depression has not been a consistent finding as with the leukocytes and thrombocytes. Slight depression of red blood counts, hematocrits, and hemoglobin has been noted at times. Bone marrow smears taken at 6 months showed no gross abnormalities. Smears taken at 8, 9, and 10 vears showed an alteration in the myeloid-erythroid ratio manifested by an increased numberof red cell precursors. Depression of peripheral blood elements in the Ailingnae and Rongerik groups was not so pronounced asin the Roneelap group. However,a slight lag in complete recovery in the Ailingnae peripheral blood count has also been noted. The persistent depression of peripheral blood elements in the exposed people makes it appear likely that thereis slight residual bone marrow damage. A general anemic tendencyhas been evident in both exposed and unexposed Marshallese. PriceJones curves, on the average, showed a slight microcytic tendency. Serum iron levels have been generally normal, and the cause of this anemic tendency has been undetermined. Reticulocyte counts have been about the samein the exposed as in the unexposed people. Chaical findings, except for radiation-induced lesions of the skin, patchy epilation, and early gastrointestinal symptoms, revealed no clear-cut disease processes or symptoms which could be re-