Chromosomal reorganization for the expression of recessive mutation of retinoblastoma susceptibility gene in the development of osteosarcoma. Recent evidence indicates that the mutation of retinoblastoma susceptibility (RB) gene is also involved in the development of osteosarcoma. We studied 30 cases of osteosarcoma for the structural anomalies of the RB gene by Southern hybridization analysis with cDNA probes of the RB gene. Thirteen cases (43%) showed structural anomalies of the RB gene. They included the total or partial deletion, or rearrangement of the RB gene; seven with homozygous deletions and six with hemizygous deletions or rearrangements. By the use of restriction fragment length polymorphism fragments as chromosome markers, those seven tumors having homozygous deletions and four of six tumors having hemizygous anomalies showed the loss of heterozygosity at other loci on chromosome 13. Among those tumors with no apparent structural changes of the RB gene, seven cases showed the loss of heterozygosity on chromosome 13, and altogether the loss of heterozygosity by either homozygosity or hemizygosity was found in 18 (64%) of 28 informative cases. The loss of heterozygosity was also found for nine of 10 other chromosomes, of which chromosome 17 showed the highest frequency (77%). The tumors with loss of chromosome 13 alleles also showed additional losses of alleles on other chromosomes, while tumors retaining heterozygosity of chromosome 13 also retained heterozygosity at the informative loci on other chromosomes. Southern hybridization and karyotype analysis in some selected cases suggest that the concerted loss of heterozygosity at multiple loci may be a consequence of the polyploidization-segregation process.