The endolymphatic sac holds the entire arrangement of immunocompetent cells and functions as an immunological potent control organ for the inner ear. The evidence of secretory immunoglobulin A and other features of lymphocyte subtypes characterizes the endolymphatic sac as an organ of the mucosa-associated lymphatic system (MALT). In this system a permanent recirculation of sensitized memory lymphocytes from one organ to the other has been demonstrated experimentally as serving to dispose memory lymphocytes after renewed antigenetic stimulus. The aim of this study was to prove the possible recirculation of antigen-sensitized lymphocytes to the endolymphatic sac after antigenic stimulus of another part of the mucosa-associated lymphatic system. The results are evidence that the endolymphatic sac is provided with immunocompetent cells which derive from the lymphatic tissue of the nasopharynx. While the origin of immunocompetent cells in the endolymphatic sac still remains uncertain, this study underlines the role of lympho-epithelial tissue of the nasopharynx as a possible cell source for the endolymphatic sac. The results might explain the altered or disturbed function of the endolymphatic sac as a possible cause of certain inner ear diseases.