Previous experiments demonstrated an organ-specific migration of sensitized lymphocytes to the inner ear and enabled us to establish an animal model for an autoimmunological labyrinthitis in the guinea pig. For a nonrandom emigration from capillaries into tissues of their immunological destination, memory lymphocytes need homing receptors on their cell surface to interact with specialized postcapillary venules, the so-called high endothelial venules. These molecules were already demonstrated in organs of the mucosa-associated lymphatic system (MALT). This study was performed to demonstrate these adhesion molecules on endothelial cells and lymphocytes of the inner ear by using two monoclonal antibodies: MECA-325 and MEL-14. Special interest was directed to the posterior spiral modiolar vein as a known port of entry for lymphocytes during an immune response. Emphasis was placed on the development of new or additional binding sites for lymphocytes on the above-mentioned structures using immunohistochemistry during an immune response of the inner ear. The results suggest a constant recirculation of memory lymphocytes through the endolymphatic sac as known for other organs of the MALT. The acquisition of high endothelial venules in the cochlea during an immune response could serve for the cellular requirements of a sympathetic cochleo-labyrinthitis with the spiral modiolar vein as port of entry for lymphocytes. Furthermore, this study supports the hypothesis of the endolymphatic sac as central immunological control organ of the inner ear and as the primary place for antigen processing.