Immunohistochemical staining of 5 gliosarcomas was performed. Neoplastic glial component stained positive by GFAP. Endothelial cells lining the lumina of glomeruloid vascular structures stained positively with both UEA-1 and FVIII/RAg antibodies. Mesenchymal cells of sarcomatous areas stained positively with SMSA antibody and presence of PDGFR. The staining results demonstrate that the sarcomatous component of gliosarcoma is of smooth muscle origin and suggest that the vascular smooth muscle hyperplasia is related to PDGF.