In mammalian epidermis a population of ATPase-positive dendritic cells, identified as Langerhans cells, has been found. Such cells are bone marrow-derived and participate in the immunological functions of the skin. We demonstrate the existence of ATPase-positive dendritic cells in separated epidermal sheets of chicken skin, by means of light and electron microscopy. They have a mean distribution of 688 +/- 265 cells/mm2 and showed several features in common with Langerhans cells. Since chickens can develop contact dermatitis, the finding is taken as the first formal demonstration of the presence of Langerhans cells in this group of vertebrates.