In vitro radiobiologic survival parameters have been determined for 7 human osteosarcoma, 5 human soft tissue and bone sarcomas, and 4 Ewing's sarcoma cell lines. The mean D0 values were 99.5 +/- 11.6 cGy, 90.5 +/- 7.7 cGy and 95.8 +/- 7.9 cGy for osteosarcomas, soft tissue and bone sarcomas and Ewing's sarcomas, respectively. These in vitro survival data do not predict the clinical radiation resistance generally attributed to osteosarcomas and soft tissue and bone sarcomas, and do not differ substantially from the results obtained with the clinically radioresponsive Ewing's sarcomas.