Oncogene amplification and expression and their mutual relationship was analyzed in 92 pediatric tumors by Southern and Northern blot hybridization with N-MYC, ERB A, ERB B, N-RAS and Shb probes. Amplification and overexpression was associated with more advanced clinical stages of tumor, especially in neuroblastomas, rhabdomyosarcomas and ganglioneuroblastomas. The most frequent alteration observed was N-MYC amplification together with overexpression. N-RAS amplification was not detected, while the overexpression of this oncogene was found in 3 cases. Neither amplification nor overexpression was revealed in any specimen of hepatoblastoma or hepatocellular carcinoma. We suggest that oncogenes overexpression provides more accurate prognostic information than amplification.