Dendritic cells were widely distributed in normal ovine skin in two main areas a) in the epidermis and epidermal appendages or in their immediate vicinity b) in the vicinity of blood vessels. It is unlikely that they represent a homogeneous population, particularly because the Langerhaps cells, which were previously discovered in all of the epidermal appendices, were located only in the epidermis using acetylcholinesterase staining. After infection with the ecthyma virus, a dense mass of closely associated dendritic cells is formed in the affected necrotic dermis, adjacent to the infected hair follicles and under the infected degenerative epidermis. These cells interact and appear to form a barrier to invasion, a framework for immune defenses and a pattern for subsequent epidermal repair; they appear to provide the foundation for a highly integrated local skin defense system.