Otitis media is the most common pediatric disease as a complication of the upper respiratory infection and at least 10% of the otitis prone children will suffer from prolonged episodes of minor conductive hearing loss and communication disorder due to the presence of middle ear effusion (MEE). In spite of exhaustive studies presented in the past three international symposia on otitis media with effusion (OME), there still remain wide gaps in our knowledge regarding the etio-pathogenesis and appropriate treatments of the disease. A couple of years ago, a new project of clinical and laboratory researches on OME were initiated in the Department of Otolaryngology, Tohoku University School of Medicine and some results of the studies have been reported in recent Japanese academy meetings as well as in the 2nd and 3rd International Symposium of Recent Advances in OME. The purpose of this paper is to summarize the results of our recent studies performed by several investigators in our department and related hospitals.