The nicotinic acetylcholine receptors (AChRs) of the skeletal muscle consist of pentameric ion channels, each of which is composed of 4 kinds of subunits. During the development of the muscle a change from a fetal type (alpha beta alpha gamma delta) to an adult type (alpha beta alpha epsilon delta) of AChR is due to the replacement of the gamma-subunit with the epsilon-subunit. We investigated the expression and transcription of the AChRs in rhabdomyosarcomas (5 cases) and in nephroblastomas with rhabdomyomatous differentiation (2 cases) by immunohistochemistry using monoclonal antibodies to the alpha-, beta- and gamma-AChR-subunit, and by mRNA dot blot and in situ hybridization applying cDNA-probes of the alpha-, beta-, gamma-, delta- and epsilon-AChR-subunit. The results indicate an intratumorous coexpression of fetal and adult types of AChRs. The presence of gamma-subunits of fetal AChRs may serve as a novel selective marker of tumors with rhabdomyomatous differentiation.