Immunocompetent cells are invariably seen in psoriatic lesions, although their role in the pathogenesis of psoriasis is not known. There are several contradictory reports about the number and function of peripheral blood lymphocytes in psoriatic patients [1, 2]. The findings in peripheral blood, however, are far from being pathognomonic for psoriasis. To the best of our knowledge there are no reports about the in situ characterization of lymphoid cell subclasses in psoriatic skin as demonstrated by modern immunohistochemical methods, except those by Haftek et al. [5, 6] concerning Langerhans cells. Oral retinoids, especially etretinate, have proved beneficial in skin disorders characterized by disturbed epidermal proliferation and keratinization [11]. The exact mode of action of the retinoids is unknown, although they are known to stimulate cytotoxic T-lymphocyte induction [3] and to affect Langerhans cells [8, 14, 15]. In order to study the involvement of Langerhans cells and lymphocyte subclasses in pso-