Rat monoclonal antibodies 3C7 and 7D4 detect two distinct functional regions of the murine interleukin 2 (IL 2) receptor. When studying the emergence kinetics of IL 2 receptors in mixed epidermal cell (EC)-lymphocyte cultures by using 3C7 and 7D4 in an indirect immunofluorescence assay, we regularly encountered a distinctive membrane fluorescence not only on lymphocytes, but also on a subpopulation of cells exhibiting a dendritic morphology. Reasoning that these 3C7/7D4-reactive dendritic cells might represent a subpopulation of epidermal dendritic cells, we studied mouse EC for the presence of 3C7/7D4- reactive cells. Although 3C7/7D4 reactivity was never detected on freshly isolated EC or on epidermal sheets, a small number of 3C7/7D4+ cells was encountered after 24 to 48 hr of culture. These cells exhibited a dendritic shape, expressed Ia antigens, lacked Thy-1 antigens, and displayed the ultrastructural features of Langerhans cells (LC) with the notable exception of Birbeck granules. Although after 24 hr, only 20% of Ia+ EC were 3C7/7D4+, the vast majority of LC displayed 3C7/7D4 binding sites after 4 to 5 days of culture. Preincubation of cultured LC-enriched EC with recombinant human IL 2 prevented subsequent 3C7-but not 7D4-binding to these cells. Western blot analysis of 7D4-reactive material of detergent extracts from LC-enriched EC revealed three bands in the same m.w. range as reported for CTLL cells. These results demonstrate that cultured LC express IL 2 receptors and may bear important implications for a better understanding of growth regulation, differentiation, and immunologic functions of LC.