Some retinoblastomas, osteosarcomas, and soft tissue sarcomas may share a common etiology. DNA and RNA were extracted from primary human osteosarcomas and soft tissue sarcomas obtained from patients without retinoblastoma and were analyzed by hybridization with a cDNA probe for RB mRNA; absence or alterations of the RB gene are associated with development of retinoblastoma. Most of the osteosarcomas or soft tissue sarcomas examined by us did not express detectable levels of RB mRNA, whereas normal cells and epithelial tumor cells did. One osteosarcoma expressed a 2.4-kilobase transcript in addition to a normal 4.7-kilobase species. Our data suggest that transcriptional inactivation or post-transcriptional down-regulation of the RB gene may be important in the etiology of some osteosarcomas and soft tissue sarcomas as well as retinoblastomas.