Two clonal fibroblast cell lines with simple chromosome aberrations-one with del(3)(p24) and the other with t(1;16)(q21;q11.2)-were established from a high dose (5.14 Gy) female atomic bomb survivor by serial culture of skin fibroblasts. These two types of clonal cells showed a more extended life span than did the cells with 44 other types of chromosome aberrations and normal cells. In addition to these results, a prominent clonal population was observed in the peripheral blood cells in this subject. It is assumed that these clonal populations arose in vivo as a result of radiation exposure to the atomic bomb.