An important role for the p53 gene in osteogenic sarcomas has been imputed by identification of somatically acquired gene alterations in human osteosarcomas and by the development of osteosarcomas in p53 transgenic mice. To study the involvement of p53 in radiation-induced osteosarcomagenesis, we have investigated gene alterations and expression of p53 in radiation-induced murine osteosarcomas and tumor-derived cell lines. Eighteen of 31 tumors and 8 of 9 cell lines showed alterations in the p53 gene region, or elevated levels of p53 RNA. Expression of the osteoblast marker gene bone gla protein was substantially reduced in tumors which simultaneously showed high steady-state levels of p53 RNA. Our data indicate that p53, in addition to its function in regulating DNA synthesis, may be involved in the control of osteogenic differentiation in osteosarcomagenesis.