[en] A series of tests of immunologic function were used in assessing the immune status of individuals who survived the atomic bombs in Japan in 1945. A-bomb survivors (n=189) residing in the US were recruited to participate in the study. Survivors exposed to varying low doses of radiation (S/sub +/ group) had healthier immune responses than those exposed to O rads (S₀ group). The difference was significant for natural cytotoxicity (p = .028). Less striking differences with the same trend (i.e., S/sub +/ healthier than S₀) were observed with: the mixed lymphocyte reactions, mitogenic response to PHA, interferon production, serum interferon levels (all S/sub +/ > S₀), frequency of detectable immune complexes, rheumatoid factor, and antimitochondrial antibodies (all S/sub +/ > S₀). In order to study the Japanese A-bomb survivors, a collaborative study was initiated with the Radiation Research Effects Foundation in Hiroshima, Japan. Immunologic tests were performed on blood samples from 278 individuals including 202 survivors of whom approximately one-third each were exposed to 0, 1-99, and 100+ rads at the time of the bomb. A decrease in immune responses was observed with increasing exposure. It is interesting that, consistent with our findings on the American survivors, the Japanese survivors exposed to 1-9 rads showed a small increase in natural cytotoxicity compared to the group exposed to 0 rads. Females showed a stronger dose-related decline than males (who may have shown a slight increase) with natural cytotoxicity, and both groups showed a small effect with interleukin 2 production. With both tests males were higher than females. Natural cytotoxicity increased significantly with age, as did serum immune complex levels. In the pilot study of the murine model for plasmacytoma formation, it was shown that age and radiation may both predispose to plasmacytoma formation. 22 references, 5 tables