Rat nephroblastoma (Wilms' tumor) was induced by transplacental administration of N-ethyl-nitrosourea (ENU). The induced renal tumors were histologically compatible with human nephroblastoma. A cultured cell line (ENU-T-1) established from a xenotransplant, showed similar morphological and biological features to cultured embryonal kidney cells. Introduction of normal human chromosome #11 (#11) bearing Wilms' tumor suppressor gene(s) (WT) suppressed colony-forming ability on soft agar plates (CFA) but tumorigenicity of ENU-T-1 was not affected. Whereas tumorigenicity of human nephroblastoma cell line, SK-NEP-1 was completely suppressed, CFA was unchanged. These facts indicated that pathogenetic mechanism is different between human and experimental rat nephroblastomas.