We report the establishment of cell lines from six radiation-induced tumors, three osteosarcomas, and three soft tissue sarcomas. Cytogenetic analysis of the lines showed mostly balanced rearrangements in the osteosarcomas; the soft tissue sarcomas had more unstable karyotypes. The rearrangements observed were unlike those previously reported for spontaneously occurring tumors of the same histological type and were more typical of the long-term changes observed after radiation exposure.