Homozygous deletion within the retinoblastoma gene in a native osteosarcoma specimen of a patient cured of a retinoblastoma of both eyes. In a native osteosarcoma specimen from a patient cured of bilateral retinoblastoma eight years ago, we found a deletion of a 7.5 kb HindIII fragment within the retinoblastoma gene. Our results contribute further evidence that the 7.5 kb fragment harbors a Breakpoint Cluster Region (BCR) in osteosarcoma. In tumor tissue of another osteosarcoma patient the retinoblastoma gene did not reveal any defect on DNA or mRNA level, suggesting different transforming events in this patient.