Pediatric solid tumors have many similarity among different tumors. These tumors present small round cell types, and cause frequent diagnostic problems in pediatric pathology. An important advance in the investigation of these small round cell tumors has been the identification of consistent chromosomal translocations associated with several types of tumor. Eighteen patients with soft tissue sarcoma were available for review. Seventeen cell lines were also included in this study. The RNA from the specimens were analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR). PAX3-FKHR fusion was present in four of five alveolar rhabdomyosarcoma and PAX7-FKHR fusion was detected in one of five alveolar rhabdomyosarcoma. None of the specimens expressed more than one chimeric transcript. EWS-FLI1 or EWS-ERG fusions were detected in all seven Ewings' sarcoma. No specimens showed EWS-WT1 fusion. These results corresponded well to the histopathologic diagnosis. There were no differences in the histologic appearances of tumors with the more frequent PAX3-FKHR or EWS-FLI1 fusions compared with those containing the variant PAX7-FKHR or EWS-ERG fusions. RT-PCR assay for chimeric transcript is an useful tool for a rapid and objective diagnosis of pediatric solid tumors. Through these tools, we can approach genetically to the differential diagnosis of undifferentiated small round tumors.