A recently developed dose-survival assay in vitro using human G0 T-lymphocytes from peripheral blood was employed to assess possible interindividual variation of cellular radiosensitivity. Currently lymphocytes from a total of 99 atomic bomb survivors were tested and D10, the X-ray dose required to kill 90% of the cells, was calculated for each test. The mean +/- SD of D10 value was 3.35 +/- 0.22 Gy for 61 survivors whose DS86 dose is below 0.004 Gy and for 38 survivors of DS86 dose above 1.5 Gy it was 3.31 +/- 0.26 Gy. So far, the results do not show any evidence in support of the hypothesis of a selective elimination of a radiosensitive subcohort among the survivors exposed to high doses.