For the purpose of clarifying the histogenesis of clear cell sarcoma of tendons and aponeuroses (CCS) as well as the problem of whether or not CCS is a heterogeneous group of neoplasms, studies based on various methods were performed. Analysis of glycosaminoglycans gave the same results for amelanotic CCS and synovial sarcoma, and the DOPA reaction gave the same negative results for amelanotic CCS and synovial sarcoma. However, the DOPA reaction was also negative in an amelanotic recurrent tumor of a melanotic CCS, and electron-microscopic studies revealed a close resemblance between amelanotic CCS and melanotic CCS. Further, enzyme histochemical studies showed definite differences between synovial sarcoma and amelanotic CCS but gave identical results for amelanotic and melanotic CCS. Immunohistochemical studies revealed the presence of S-100 protein in all CCS cases, both amelanotic and melanotic. These results indicate that CCS is not a heterogeneous group of neoplasms, and that both amelanotic and melanotic CCS are of neural crest origin.