Otitis media with effusion (OME) is a very common pediatric disease with unknown etiology which sometimes leads to chronic recurrent OME. Immune reactions in serum and in the middle ear system play roles in the etiology, pathogenesis, and prevention of otitis media. The middle ear mucosa has a secretory immune system similar to those of other areas of the respiratory tract, except that it does not have lymphoid follicles. Otitis media with effusion (OME) is very common in pediatric patients. Immune reactions in serum and middle ear system play roles in the etiology, pathogenesis and prevention of otitis media. Immunologically active antigens interact with immunocompetent cells in the lamina propria of the middle ear to produce a local immune response. In this investigation, 32 sera and 50 middle ear fluid samples from children (ranged 1 to 10 years) with secretory otits media were analyzed for IgA, IgM, IgG, C3 and C4 by single radial immunodiffusion (SRID) and IgE by enzyme linked immunosurbent assay (ELISA) techniques. Our results indicated a highly significant increase in IgA and a decrease in IgM, IgG, IgB, C3 and C4 in secretion as compared to serum concentrations. The ratio of IgAJIgG, a valuable index of local immune response, was higher in the middle ear than in serum. These data support the hypothesis that there is an independent mucosal immune response in the middle ear mucosa to different stimuli.