Morphological characteristics of tactile-like corpuscles (tactoid bodies, pseudomeissnerian corpuscles) which are occasionally present in neurofibromas have already been detailed. However, there has yet been controversy on the cytogenesis of these lamellated structures. Probably, one of the most important problems is whether tactile-like corpuscles are composed of Schwann cells or of perineurial cells. In this study, seven cases of neurofibromas with tactile-like corpuscles were examined by rabbit or mouse polyclonal antisera to S-100 protein which could be regarded, at least in the peripheral nervous system, as a specific marker for Schwann cells. Since recent extensive studies have revealed that S-100 protein is a mixture of two predominant dimeric components with S-100 alpha and S-100 beta subunits, and the S-100 alpha subunit is absent from Schwann cells, tactile-like corpuscles were also examined by a mouse monoclonal antibody (ASA-1) specific for the S-100 alpha subunit. For immunohistochemical analysis, peripheral nerves, Meissner corpuscles and epidermal melanocytes were also examined in parallel. By the immunoperoxidase method using rabbit or mouse polyclonal antisera to S-100 protein, tactile-like corpuscles were intensely stained in sections from all seven cases. Both the flattened cell bodies and the eccentrically located nuclei of their constituent cells were stained. In the background neurofibroma tissue surrounding the tactile-like corpuscles, spindle-shaped cells were stained variably. In three of the seven cases, numerous melanin-containing cells which often surrounded the tactile-like corpuscles were also stained. In normal peripheral nerves, positive staining was confined to Schwann cells and their processes.(ABSTRACT TRUNCATED AT 250 WORDS)