Most of these methods have not been used in previous experiments. We analyzed the protein composition of the inner ear fluid of diseased and control groups to find evidence suggesting that increased immune or inflammatory reaction is involved in the pathogenesis of Meniere’s disease. Proteomic techniques were used to analyze the protein constituents of the inner ear fluid. We used ES luminal fluid because the protein concentrations in this fluid are very high and because the ES is the site where most immunologic reactions occur in the inner ear. In addition, sampling the ES luminal fluid does not usually affect inner ear function; indeed, the 3 patients enrolled in this experiment who underwent ES surgery had preserved inner ear functions after sampling. The use of cochlear and vestibular endolymph in addition to ES luminal fluid would have improved our study; however, sampling the cochlear and vestibular endolymph in patients with Meniere’s disease would have been impossible because the inner ear function of the patients would have been destroyed and the protein concentrations in these compartments would have been too low for the analysis. The most commonly encountered proteins in the ES luminal fluid were immunoglobulins and their variants. This is expected, as the ES is a known site of immunologic responses in the inner ear. However, the only proteins that were detected exclusively in the patients with Meniere’s disease were immunoglobulins, their variants, and interferon gamma regulatory factor, suggesting that increased inflammatory reactions in the inner ear may contribute to the pathology of Meniere’s disease. The increased inflammatory reaction could be caused by various etiologies such as allergy, viral infection, genetic cause, or autoimmunity. Although direct evidence of autoimmunity was not found in the luminal fluid analysis, our results about the presence of circulating autoantibodies and increased immune reaction between patients’ sera and mouse inner ear tissue could Epoxomicin support the possibility of autoimmunity as a cause of increased immune/inflammatory reaction in the inner ear. If autoimmunity was the cause of the increased inflammatory reactions the autoantibodies responsible for these reactions have a molecular weight between 17 and 26 kDa and between 55 and 63 kDa as revealed by LC-MS/MS in our results. Evidences for autoimmune reactions in the inner ear of patients with Meniere’s disease have been reported. One report demon strated the presence of focal inflammation with intraepithelial invasion by mononuclear cells in the ES of patients with Meniere’s disease that altered the normal structures in the endolymphatic sac.