Four cases of Riehl's melanosis were studied with light and electron microscopes. The results obtained were as follows: Unmyelinated nerve fibers were found in both the epidermis and the dermis, and the Schwann cells enclsing the axons contained melanosomes. A peculiar pigment cell was found in the epidermis, it was thought to be a macrophage phagocytizing melanosomes from the extracellular spaces. A melanophage in contact with a keratinocyte through the gaps of the basal lamina was observed. It was suggested that all these processes might participate in pigmentary incontinence in Riehl's melanosis. At the dermo‐epidermal junction the basal lamina was multilayered. In the upper dermis a large number of melanophages were present, and in addition, amyloid islets and fibrillar masses resembling the “fibrilläre Körper” were observed.

Langerhans cells in the epidermis at the sites of vaccina virus inoculation were studied with the electron microscope. The cells contained unusually increased numbers of the Langerhans cell granules. Such abnormal Langerhans cells have not been described except for in histiocytosis X. Vaccinia virus particles were found in the Langerhans cells, where they were located individually or embedded in the granular matrix or in lysosomes.

Three cases of basal cell epithelioma were studied with light and electron microscopy. Myofibroblasts, some containing melanosomes, were observed in the stroma of the tumors. The significance of these cells in the tumor is briefly discussed.

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