We studied the expression of the dbl oncogene in the total RNA obtained from a wide spectrum of childhood tumors, including Ewing's sarcomas, peripheral neuroectodermal tumors (PNET), esthesioneuroblastomas, neuroblastomas, retinoblastomas, rhabdomyosarcomas, osteosarcomas, and synovial sarcomas. Material was obtained from primary tumors, nude mice xenografts, and tumor cell lines. Following the Northern blot technique, a single band of 2.8 kb was found in each analyzed case. Induction of neural differentiation in Ewing's sarcoma, peripheral PNET, and neuroblastoma cell lines with dibutyryl cyclic AMP did not change the expression of the dbl oncogene. We conclude that the wide expression of the dbl oncogene in these childhood tumors reduces its value as a molecular marker for their differential diagnosis; on the other hand, the dbl oncogene does not appear to be an essential molecular factor in the process of neuroectodermal differentiation of small round cell tumors of childhood.