Effects of fall-out radiation on Marshallese 273 level of the unexposed comparison population during the first two months, but did not result in any observable untoward effects in the people. No increased incidence of infection was observed, and no therapy (antibiotic or otherwise) was given specifically for their leukopenia. Mean blood-platelet levels were also significantly depressed to about 30 per cent of the unexposed levels by the fourth week. No bleeding associated with the platelet depression was noted, and no blood transfusions were necessary. Erythrocytes as measured by haematocrit levels were not significantly depressed. Following this early depression, the blood elements slowly recovered, some elements faster than others. The neutrophils were first to reach comparison population levels by about one year post-exposure(figure 2). The lymphocytes returned more slowly, and even at two and three years’ post-exposure the mean levels were slightly below the unexposed meanlevels (figure 3). By four years they had reached the unexposedlevels and remained so at the time ofthe five-year survey. Platelet levels showed the slowest recovery (figure 4). A rapid recovery trend followed the early depression, after which there was slower increase with mean levels remaining consistently below the unexposed mean population level. At the five-year survey the males were about 13 per cent and the females 11 per cent below the corresponding mean levels of the comparison population, though the individual platelet counts were within the normal range. The mean red blood count, haemoglobin and haematocrit levels, were about the same in the exposed as in the unexposed group. The 18 Rongelap people who had received about 70 r at Alinginae Island showed less severe early haemopoietic depression, but have also shown a similarly slow recovery rate of lymphocytes and platelets, as noted in the more heavily exposed group. The incidence of diseases, infectious or non-infectious, has remained about the same in the exposed as in the unexposed population. Three deaths have occurred: one in a 46-year-old man during the second year after exposure from hypertensive heart disease which had been present at the time of exposure; the second in a 78-year-old man, at three years after exposure, of coronary heart disease complicating diabetes; and the third in a 36-year-old man, at four years after exposure, of acute varicella. During thefirst six weeks over half of the exposed people lost weight, even though their diet was satisfactory and appetites good during this period. This possibly reflects an effect of radiation exposure on general metabolism. However, factors associated with a change in environment cannot be ruled out as being responsible. There were no abnormalities noted at birth in four babies irradiated in utero; two in the first trimester, one in the second trimester, and one in the third trimester. The five-year survey revealed that the people were generally in a goodstate of health and nutrition. The incidences of diseases were about the samein the exposed and unexposed groups. One case of ovarian cancer developed during the past year in a 61-year-old exposed woman. 2.2. Late effects of gamma-radiation Late effects of radiation exposure constitute an important part of the examinations in the Marshallese. Very little is known about such effects in