Langerhans cells (LC) in epidermis are antigen presenting cells. LC may play a role in immune surveillance system and are considered to suppress development of ultraviolet (UV) induced skin cancers. We studied effect of UVB irradiation to LC of xeroderma pigmentosum (XP) and normal subjects by using OKT6 monoclonal antibody. When 3 minimal erythema dose (MED) of UVB were irradiated, density of OKT6 positive LC of XP began to decrease 6 hours after irradiation, and showed the least numbers on day 2 and returned completely to the pre-irradiation level on day 14. Further, after 3 MED irradiation, LCs of both normal subjects became the least on day 3 and returned to the pre-irradiation level on day 14. In XP variant and normal subjects, the number of LC in chronic sun-exposed skin decreased significantly in a similar way comparing to that of non-exposed skin. These results suggest that epidermal LC may not play an essential role in prevention of UV-induced tumor development.