During the past several. years we have extended these studies to include ; an examination of some aspects of the immune status in the exposed and unexposed Marshallese populations which might be indicative of aging and/or radiation exposure. The present studies include measuring transformation and replication . _of circulating lymphocytes from phytohemagglutinin (PHA) stimulation in culture, quantification of the various serum proteins by electrophoresis, immunodiffusion Studies for immunoglobulin levels, and routine enumeration of peripheral blood ‘elements. In contrast to results of previous studies some of the present tests showed differences in the exposed population compared with the unexposed group © that might beinterpreted as radiation effects. Therefore in this report the “results in the unexposed population will be treated separately to determine - t the correlation of these criteria with aging in a normal Marshallese population, The results in the exposed group will then be compared with the unexposed group to evaluate possible radiation effects. MATERIALS AND METHODS In Table 1 the numbers of subjects on whom the various tests were done are listed according to age decades. Lymphocyte cultures. - Blood cultures were set up as follows. The buffy coat ° was separated from 5 ml of heparinized blood by sedimentation and centrifugation, The culture medium consisted of Eagle's minimum essential medium supplemented with 1% glutamine, 15% fetal calf serum, penicillin (100 units/ml), and streptomycin (0.1 mg/ml). . K Five-ml cultures were seeded with 106 leukocytes/ml, -PHA M Difco (0.32 mg/ml culture) was added and the cultures were incubated at 37 C. At exactly 72 hr the cells were harvested, and the number of transformed lymphocytes (blast-like cells) was determined as follows. The cells were | prepared for counting by the method of Stewart and Ingram (1968). A 1-ml aliquot of each culture was treated with a proteolytic enzyme (pronase) to remove i l ! i