The middle ear effusion is one of the most common disease in children but its pathogenesis in not clear. Recently, a hypothesis of adenoid mediator release was introduced based upon the immunologic aspect of the adenoid. We focused on the adenoid mast cell in the pathogenesis of the middle ear effusion based on the fact that histamine level of the adenoid with middle ear effusion is higher than that without middle ear effusion. After fixation of adenoid specimen with Carnoy's fixative and formalin, 0.5% toluidine blue staining was done. The number of the mast cell in the connective tissue and epithelium of adenoid tissue was counted and degranulation rate was calculated. The number of the mast cells was not significantly different between MEE group and control group but degranulation rate was significantly higher in the patient with secretory otitis media.