We have recently concluded from a clinicopathologic study on childhood rhabdomyosarcoma (RMS) that there is a great biologic difference between the embryonal and alveolar histologic subtypes of RMS. To confirm this observation on an experimental basis, we will inject the subcutis and tail vein of nude mice with cells of both subtypes of RMS, from well-established cell lines and will observe their tumorigenicity and metastatic potential. The resulting tumors will be processed for paraffin and EM blocks and for frozen section analyis and in situ hybridization.