Identification of growth factors and receptors in mesenchymal tumors may be crucial to understanding of growth regulation in sarcomas. During an immunohistochemical study of the expression of growth factors and receptors in human soft tissue tumors (STT), only 1 antisera capable of working in paraffin-embedded tissue was noted. A detailed study of 141 STT was undertaken to determine the frequency of expression of nerve growth factor receptor (NGF-R), its specificity and sensitivity for neural tumors, and the effect of fixation on detection. In normal mesenchymal tissue, only nerve sheath and perivascular staining was seen. No immunoreactivity was seen in many tumors including rhabdomyosarcoma, angiosarcoma, liposarcoma, Ewing's sarcoma, and alveolar soft part sarcoma. Less than 15% of tumors of smooth muscle, fibrous, or fibrohistiocytic origin showed immunoreactivity, usually focal. In contrast, a high frequency of immunoreactivity was noted in tumors of neural origin (74%). This included granular cell tumors (100%), Schwannoma/neurofibroma (91%), malignant Schwannoma (78%), neuroblastoma/neuroepithelioma (60%), and paraganglioma (57%). A high rate of reactivity was also seen in synovial sarcomas (80%), undifferentiated sarcomas (60%), and hemangiopericytomas (43%), suggesting a potential relationship to the neural phenotype. Among the neural tumors, Bouin's fixation was superior to formalin, suggesting that immunoreactivity for NGF-R is affected by fixation. This antibody may be a useful adjunct marker diagnostically.