Histologic and immunochemical analyses were performed on 38 cases and 33 cases of malignant tumors of the peripheral nerve sheath, respectively. The histologic features consisted of either closely packed or loosely arranged interlacing fascicles of slender spindle cells that showed a wavy pattern. Although no characteristic findings indicative of neurogenic differentiation could be confirmed with anti-S-100-protein, a fair number of positive cells were seen in the area where the tumor cells were loosely arranged and displayed a wavy pattern. When anti-neuron-specific enolase (NSE) and anti-neurofilament antibody (68K, 200K) were applied, they were found to be positive in cells differentiating to ganglion cells and in epithelial cells. Since S-100-protein-positive cells indicate a differentiation to Schwann cells and NSE-positive cells and neurofilament-positive cells to nerve cells, it was concluded that immunohistochemistry can serve as an effective supplementary method for the diagnosis of malignant tumors of the peripheral nerve sheath.