A 57-year-old man, who had received injections of an arsenide for the treatment of syphilis, developed a tumor on his lower lip and a patchy pigmented lesion on his neck 2 years before the present examination. The lesions enlarged progressively. Under a diagnosis of arsenical keratosis and Bowen’s disease associated with chronic arsenicism, light and electron microscopic observations were made of the lesions. Vacuolated cells were demonstrated by light microscopy, while the characteristic electron microscopic features of both lesions were the appearance of nuclear bodies and the presence of radially arranged, intranuclear inclusion bodies of high electron density.