At adenoidectomy specimens for bacteriological, virological, and histological investigation were obtained from the adenoids of 144 children, 53 of whom suffered from otitis media with effusion, or frequently recurring otitis media. Comparison of findings in the children with ear diseases with those obtained in the rest of the material showed that Hemophilus influenza was cultured from 50% of the specimens from the children with ear diseases, while only 14% of the cultures from the other children yielded H. influenza. Virus isolates were made from 17 adenoids. In children with ear diseases a virus was isolated from 28% of the specimens, whereas positive isolates were obtained in only 3% of the rest of the specimens. Both findings are statistically significant and support the view that the adenoid tissue may play an important role in the etiology of otitis media with effusion. The infected adenoid may be the direct source of the primary infections, or continuous microbial irritation in the nasopharynx may indirectly be the cause of otitis media with effusion, as persistent infection and edema maintain chronic dysfunction of the eustachian tube. Thus adenoidectomy may be beneficial in the treatment of frequently recurring otitis media, preventing otitis media with effusion from developing.