AbstractUsing OKT6 monoclonal antibody (MCA) and β‐specific anti‐S‐100 protein (S‐100β) MCA, the numbers of Langerhans cells (LC) in the epidermis overlying squamous cell carcinoma (SCC), basal cell epithelioma (BCE), dermatofibroma (DF), and in the lesional epidermis of seborrheic keratosis (SK) were investigated. The numbers of LC were significantly increased in the epidermis overlying SCC and in SK. Moreover, significantly more LC were observed in the epidermis overlying SCC than in SK. The increased density of LC in the epidermis overlying SCC may suggest participation and activation of the mononuclear phagocyte system in this neoplasm. In 8 cases of SCC, the subpopulations of infiltrating lymphocytes around the tumor cell nests were analyzed. The ratio of Leu 3a‐positive cells/Leu 2a‐positive cells ranged from 0.63 to 1.99. This diversity may reflect complicated immunological interaction between the tumors