levels of leukocytes and platelets of the peripheral blood. This was most marked in the 64 people on Rongelap who had received 175 rads, and wasless markedin the other groupsreceiving less exposure. The hemopoietic depression was roughly proportional to the dose of radiation received. Evenin 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 showedperipheral 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 Utirik 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% ofthe levels in the comparison children, but showed slight rise during the following weeks. The depressed level was maintained with only slight increase noted by one year. In thefollowing year, mean counts approachedthelevels 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 burnsof the skin during that period. Neutrophil depression becameevident by 5 and 6 weekspost exposure with levels reaching about half that of the comparison population in the adults andslightly lower in the children <3 yearsof age. This degree of neutropenia wasinsufhicient to result in any apparentincreased infectious processes, and indeed it was noted that neutro- philic leukocytosis was possible in people showing casualinfectionsat this time. Neutrophillevels recovered more rapidly than lymphocyte levels and reached nearcontrol levels by one year. Subsequent annual surveys have revealed that recovery does not appear to be complete, particularly in youngerandolder age groups. Platelet counts showedless fluctuation than other blood counts andfairly consistently showed in- creasing 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 56Gb 185 weeks, which was followed by slower recovery but with meanlevels never reaching higher than 90 to 95% that of the comparison population during the 8 years post exposure. Erythropoietic 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. No gross 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 myeloid-ery- throid ratio wth abnormalities of the erythroid and myeloid precursorsin 5 cases. Depression of peripheral blood elements in the Ailingnae and Rongerik groups was not so pronounced as in the Rongelap group. However, a slight lag in complete recovery in the Ailingnae peripheral blood counthasalso been noted. The persistent depression of peripheral blood elements in the exposed people makesit appear likely that there is slight residual bone marrow damage. A general anemic tendency has been evidentin both exposed and unexposed Marshallese. PriceJones curves, on the average, showed 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 therapy of radiation effects was ever con- sidered necessary or given. Epidemics of chicken pox and measles that occurred showed no greater incidenceor severity in the exposed than in the unexposed Marshallese people. Duringthefirst months post exposure abouthalf of the exposed group exhibitedJoss ofweight of several pounds. This may possibly have been related to their radiation exposure, althoughit is difficult to rule out effects possibly due to change of environment. At3 years post exposurethe zmmuneresponseto pri- mary and secondarytetanusantitoxin was tested and found notto besignificantly different in the exposed compared to the unexposed populations.