We examined in vivo and in vitro expression of nerve growth factor (NGF) receptors in 13 dermal and 9 plexiform neurofibromas, 28 schwannomas, and 4 traumatic neuromas with an immunohistochemical method using a monoclonal antihuman NGF receptor antibody (ME20-4) and anti S-100 beta protein antibody. Immunoreactivity for NGF receptor and S-100 beta protein was universally observed on the principal cells of both neurofibroma and schwannoma in vivo. Moreover, we examined the NGF receptor and S-100 beta protein immunoreactivity in the culture system of the neurofibroma and schwannoma with an immunofluorescent double staining method. The principal cells of both tumors were positively stained by both ME20-4 and anti S-100 beta protein antibodies. These cells also express the ability for 125I-NGF binding, which was examined with an autoradiographic technique. These results suggest that NGF receptors are universally expressed on the S-100 beta protein positive Schwann-like cells composing of these tumors both in vivo and in vitro. In traumatic neuroma, however, a positive staining of NGF receptor was more strongly observed in the perineurium rather than in the endoneurial cells.