Cytogenetic and restriction fragment length polymorphism (RFLP) analyses were performed on a mediastinal germ cell tumor comprising distinct teratoma and embryonal rhabdomyosarcoma components in a 31-year-old male and a hepatoblastoma in a 2 month-old male child. Clonal relationship between the teratoma and rhabdomyosarcoma of the germ cell tumor was established by the presence in both of i(12p), the characteristic marker of germ cell tumors. Both the rhabdomyosarcoma component of the mediastinal germ cell tumor and the hepatoblastoma exhibited rearrangements of 2q. These data suggest that malignant differentiation of a teratoma is accompanied by the development of chromosome abnormalities specific for the transformed histology and further suggest that 2q abnormalities may be the common genetic link in the development of the two histologically unrelated tumor types, embryonal rhabdomyosarcoma and hepatoblastoma.