Soft tissue sarcomas have been examined for alterations in the p53 gene. In six sarcomas, loss or rearrangement of both alleles of this gene was detected while in a further seven sarcomas, point mutation or absence of transcription of the p53 gene was observed. Abnormalities of the p53 gene were found in several classes of soft tissue sarcoma, including leiomyosarcomas, rhabdomyosarcomas and malignant fibrous histiocytomas. Our studies also show that abnormalities of the RB1 suppressor gene and of the p53 gene frequently occur together. These results are consistent with the idea that the p53 gene is a tumour suppressor gene and indicate that coincident inactivation of more than one tumour suppressor gene may, in some cases, be required for tumour development.