above 5% in about half of the people of both groups. 6. Hematocrit. Erythropoeitic activity as evidenced by hematocrit readings has not shown any remarkable change since exposure. The values have been consistently on the low side of normals, according to American standards, particularly in the females in both exposed and unexposed people. The hematocrit readings after 4 years were about the same as found at 3 years and about equal to the comparison population level. B. Physical findings 1. Diseases. There have been no diseases, infectious or non-infec- tious, that could be related to irradiation effects. No antibiotics, blaod transfusions, or other specific therapy has been used either prophylactically or therapeutically in the Marshallese, even during the acute period when maximum depression of the blood elements was noted. The incidence of dise eases in both the exposed and comparison populations has been about the same. Even when leukocyte depression was greatest (the levels reaching about half of the levels of the comparison population at about 5 to 6 weeks post~-exposure) there was apparently no increased susceptibility to infection. An epidemic of upper respiratory infection that occurred at this time showed no greater incidence or severity in the exposed people compared to the unexposed. There was no bleeding associated with a maximum depression of platelets (11 indie viduals had platelet counts between 35,000 and 65,000). The people have since sustained epidemics of measles, chicken pox, upper respiratory infections, and gastroenteritis without untoward reactions. A limited study of the immine response at 3 years post-exposure showed that the antibody ree sponse to tetanus toxoid antigenic stimulus was not significantly different in the exposed and unexposed people at that time. During the past year 5 exposed children and 1 unexposed child presumably had infectious hepatitis. No other serious illnesses were reported. “7a