Two skin biopsies of lymphadenosis benigna cutis have been analyzed by morphological and immunological methods using monoclonal and polyclonal antibodies on cryostat and paraffin sections. Follicular structures containing active germinal centers are composed of identical cell types as germinal centers of normal lymphatic tissue, e.g. centrocytes, centroblasts, immature plasma cells, dendritic reticulum cells and some T lymphocytes. Outside and inbetween the secondary follicles the infiltrate is composed of small T lymphocytes (OKT-3+, focal positive acid phosphatase reaction). Among T lymphocytes the OK.T-4+ to OKT-8+ ratio was 2:1. Within these areas, consisting almost exclusively of T lymphocytes, cells with electron microscopical features of indeterminate cells and interdigitating reticulum cells were recognized. Those cells are OKT-6+. It can be concluded that in lymphadenosis benigna cutis the infiltrate of the dermis is composed of B and T cell areas which show the same microarchitecture and morphology as in normal lymphatic tissue.