Dendritic cells (DC) are considered to be the most potent antigen-presenting cells, and CD83 is expressed at a high level on immune-competent, activated and mature DC. Although changes in the number or localization of mature and activated CD83+ DC could be expected in psoriasis, there is little information on such changes. Morphological identification of CD83+ DC in psoriatic skin lesions. Immunohistochemical staining was performed in 5 specimens of psoriasis vulgaris and 6 specimens of pustular psoriasis. Formalin-fixed, paraffin-embedded sections were used for examination in this study. The skin sections were pretreated with 0.1% trypsin for 60 min at 37 C prior to immunostaining for CD83. A small but significant subpopulation of CD83+ DC was found in the upper dermis. In addition, CD83+ DC were occasionally scattered in the epidermis. The most common distribution pattern of CD83+ DC was as clusters with mononuclear lymphoid cells in the upper dermis. CD83+ DC were in close contact with lymphocytes. High-intensity staining of CD83 antigens was detected not only on the surface, but also in the cytoplasm of DC. These results indicate that activated and mature CD83+ DC may play a role in the immune response in psoriasis and provide in vivo support for the concept that CD83+ DC provide signals for direct intralesional T cell activation.