The CD11/CD18 family of leukocyte adhesion-promoting proteins is comprised of three members, each composed of a shared beta subunit (CD18) noncovalently associated with unique alpha subunits (CD11a, CD11b and CD11c respectively). Such three heterodimers, named LFA-1 (CD11a/CD18), H-Mac-1 (CD11b/CD18) and gp150,95 (CD11c/CD18), are involved in mediating leukocyte adhesion in virtually all phases of the immune responses. Since Langerhans cells are regarded as cutaneous leukocytes, we investigated the expression of the members of the CD11/CD18 family on Langerhans cells. A vast series of immunostaining procedures was carried out, using monoclonal antibodies anti-CD11a, -CD11b, -CD11c, and -CD18. Normal skin frozen sections and epidermal sheets were investigated by immunohistology and immunofluorescence; suspended freshly isolated epidermal cells were processed using immunogold techniques, performed in both transmission and scanning electron microscopy, including double labeling procedures and semiquantitative analysis of the labeled cells. The results demonstrated the expression on the membrane of Langerhans cells of the CD11b, CD11c and CD18 antigens, thus indicating that at least both the H-Mac-1 (CD11b/CD18) and the gp150,95 (CD11c/CD18) members of the CD11/CD18 family are detectable on the cell surface of human resting Langerhans cells. Since both such moieties serve as adhesion molecules in (a) cell-cell interactions and in (b) leukocyte migration and localization, the present results suggest that H-Mac-1 and gp150,95 might display a key role (a) in promoting interactions between Langerhans cells and other cells, and (b) in guiding the migration and localization of Langerhans cells.