In this report we have employed an alternative tissue-sectioning procedure which provides a plan view of intra-epithelial cell populations within the airway wall. Immunoperoxidase staining of such sections for class II MHC (Ia) antigen revealed the presence of a highly developed intra-epithelial network of Ia-positive dendritic cells, which was not evident employing conventional cross- or longitudinal tissue sections. This finding has important implications for the study of mechanisms underlying allergic and infectious diseases of the respiratory tract.