When screening skin cryosections with a panel of monoclonal antibodies (MoAb), we found that the anti-CD69 MoAb Leu-23 reacted with a subpopulation of epidermal dendritic cells, presumably Langerhans cells (LC). The staining intensity was enhanced by gentle trypsin pretreatment of the sections. Flow cytometric analysis of LC-enriched epidermal cells (EC) revealed that nearly all CD1a-bearing LC display anti-CD69 reactivity when tested briefly after termination of the enrichment procedure. Immunoprecipitation experiments showed that isolated LC specifically express a disulphide-linked dimer composed of 26/30kDa subunits that therefore slightly differs from the 28/32kDa CD69 complex described on activated T or natural killer (NK) cells. This difference is probably due to a different post-translational glycosylation pattern as evidenced by Endoglycosidase-F treatment of the immunoprecipitate disclosing the 24-kDa core protein of CD69. When freshly isolated LC-enriched EC were kept in culture, anti-CD69 reactivity gradually decreased but the addition of IFN-gamma to the culture medium sustained the CD69 expression on LC in vitro. These results strongly suggest that resident but not LC recovered from EC cultures bear CD69 moieties. It remains to be seen whether the expression of this antigen can be linked to (a) particular functional property (ies) of intraepidermal LC.