Human leukocyte antigen (HLA) phenotypes were studied in twenty Japanese patients who had typical osteosarcoma. The HLA-A11 phenotype was found in ten (50 per cent) of the twenty patients, compared with 16.6 per cent of 235 control subjects (chi square = 13.248; p less than 0.0005)--an odds ratio of 5.026. These data suggest that major histocompatibility complex-linked genes may determine susceptibility to osteosarcoma.