Forty-eight benign and malignant soft tissue tumors were investigated immunohistologically for the presence of laminin, a glycoprotein of basement membranes. The results showed intense laminin positivity in schwannomas and neurofibromas and less intense positivity in leiomyomas and leiomyosarcomas, whereas fibrous histiocytomas and fibrosarcomas generally were negative. It is suggested that immunohistochemical demonstration of laminin is a valuable aid in the differential diagnosis between tumors derived from fibroblasts and Schwann cells, and a potential aid in the differential diagnosis between tumors originating from fibroblasts and those from smooth muscle cells. In addition to the expression seen in the tumors, all vascular walls were positive for laminin. Therefore, demonstration of laminin also can be used to examine the vascular pattern of tumors.