The expression of human nerve growth factor (NGF) receptor in tumors and normal tissue was investigated with the use of a monoclonal antibody recently developed against that protein. This antibody, NGFR5, reacted strongly with 100% of 25 nerve sheath tumors. Eight of nine pheochromocytomas and three of three paragangliomas also had positive results, but the immunoreactivity was restricted to the sustentacular cell population. Within cells of melanocytic lineage, there was no immunostaining of melanocytes in normal epidermis, whereas 13 of 14 benign nevi had positive results, primarily involving spindled nevocytic structures within the dermis. NGF receptor was scarcely expressed in human melanoma; 9 of 19 melanomas had positive results, but immunoreactivity was generally restricted to rare cells within the larger tumor cell population. Among nonneurogenic mesenchymal tumors, results were generally negative: 0 of 5 chondrosarcomas, 0 of 6 malignant fibrous histiocytomas, 0 of 3 meningiomas, and 1 of 8 leiomyosarcomas were immunoreactive. Carcinomas were variable in immunoreactivity: 12 of 16 squamous cell carcinomas had positive results, whereas adenocarcinomas demonstrated focal, basal epithelial immunoreactivity and neuroendocrine tumors generally had negative results. Among normal tissues, in addition to expected neural immunostaining, NGFR 5 reacted positively with several nonneural cell types, including lymphoidal follicular dendritic cells, myoepithelial cells, vascular adventitia, and basal epithelium of oral mucosa and hair follicles. Antibodies to NGF receptor may play a role in the identification of benign and malignant soft tissue lesions.