levels of leukocytes and platelets of the peripheral blood. This was most marked in the 64 people on weeks, wr zh was followed by slower recovery but with mea.. .evels never reaching higher than 90 to sure. The hemopoietic depression was roughly proportional to the dose of radiation received. Even in the 157 Utirik people who received only 8 years post exposure. Erythropoietic depression has not been a consistent finding as with the leukocytes and thrombocytes. Slight depression of red biood counts, hema- Rongelap who hadreceived 175 rads, and was less marked in the other groups receiving less expo- an estimated | 4 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 exposure groups. The chronological records of blood findings in the Rongelap and Ailingnae groups are presented in Figures 20, 27, and 32 and in Appendices | and 2, and in the Uuirik group in Appendix 3. Lymphopenia of about half the level of the comparison Marshallese population was evident when the Rongelap people werefirst examined on their arrival at Kwajalein 3 days after exposure. 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 depressed level was maintained with only slight increase noted by oneyear. In the following year, mean counts approached thelevels of the comparison population and have generally remainedslightly below. 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 becameevident by 3 and 6 wecks post exposure with levels reaching abouthalf that of the comparison population in the adults andslightly lower in the children <5 years of age. This degree of neutropenia was insufficientto result in any apparent increased infectious processes, and indeed it was noted that neutrophilic leukocytosis was possible in people showing casualinfections at this time. Neutrophillevels re- covered more rapidly than lymphocyte levels and reached near controllevels by one year. Subsequent annual surveys have revealed that recovery does not appear to be complete, particularly in vounger and older age groups. Platelet counts showed less fluctuation than other blood counts and fairly consistently showed in- creasing depression, reaching levels 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 95% that of the comparison population during the tocrits, and hemoglobin has been noted at times. Nogross abnormalities of bone marrow smears were reported at 6 months post exposure. At 8 years, examination of 9 bone marrow aspirations from exposed people showed a reduced mveloid-erythroid ratio wth abnormalities of the erythroid and myeloid precursors in 5 cases. Depression of peripheral blood elements in the Ailingnae and Rongerik groups was not so pro- nounced as in the Rongelap group. However, a slight lag in complete recovery in the Ailingnae peripheral blood counthas also been noted. The persistent depression of peripheral blood elements in the exposed people makes it appear likely that there is slight residual bone marrow damage. . A general anemic tendency has been evidentin both exposed and unexposed Marshallese. Price- Jones curves, on the average, showed a slight microcytic tendency. Serum iron levels have generally been normal, and the cause of this anemic tendency has been undetermined. Reticulocyte counts have been about the same in the exposed as in the unexposed people. Exceptfor radiation-inducedlesions of the skin, patchyepilation, and early gastrointestinal symptoms, clinical examinations have revealed no disease processes or symptoms which could be related directly to radiation effects. No prophylactic or specific therapyof radiation effects was ever considered necessary or given. Epidemics of chicken pox and measles that occurred showed no greater incidence or severity in the exposed than in the unexposed Marshallese people. Duringthe first months post exposure abouthalf of the exposed group exhibited Joss of wezghtof sev- eral pounds. This may possibly have been related to their radiation exposure, althoughitis difficult to rule out effects possibly due to change of environment. At3 years post exposure the zmmuneresponse to primary and secondary tetanus antitoxin was tested and found notto be significantly different in the exposed compared to the unexposed populations.