A serious anaerobic sampling and cultivation technique was used in order to obtain representative samples from 45 middle ear effusions in 30 patients with longstanding secretory otitis media (SOM). Despite the fact that an accurate sterilizing procedure was performed, 16 % disclosed contaminated samples from the ear canal and tympanic membrane. Among the remaining samples, middle ear bacteria were found in 30 % of which Staphylococcus epidermidis and Haemophilus influenzae contributed to the major part. Anaerobes were only occasionally found. The amount of bacteria found was sparse in all cases. It can be concluded that the inflammatory process in SOM is not maintained by anaerobic bacteria within the middle ear cavity.