Light microscopic observation of resected specimen of Synovial Sarcoma was carried out on 51 cases

among which 2 cases were studied by electron microscope and 10 cases by imm-unochemical keratin protein stain simultaneously. Light microscopic observation showed that all of the cases possessed biophasic differentiation in various degrees. They could be devided into four groups: (1) Epithelium type

(2)

Spindle cell type

(3) mixture type

(4) Small round cell type. Electron microscopic observation of 2 cases showed that there were desmo-somes

interdigitation and filopodia(microvilli) on the surface of the epithelial component of the tumors. One of the two cases contained tonofilament in its plasma. Immunochemically

keratin protein stain was positive in 7 of the ten cases observed. Histogenesis of tumor cell was discussed. Evidence of observation suggested that it is possible that the cell could be derived from mesodermal cell. That some of the 51 cases could be named as carcinosarcoma is acceptable