Cytochemical, ultrastructural and immunological properties of human Schwann cells were studied in normal adult and foetal nerve sections and in tissue cultures. As specific markers for Schwann cells we used S-100 protein and laminin. The presence of Sudan black-positive, Oil Red-O-negative material was found in Schwann cells in vitro. Structural features, examined at E.M. level, are described. This information may be useful in nerve tissue culture studies, a new tool for the investigation of dyschwannian neuropathies.