\s=b\Bacteriologic investigation of middle ear effusion (MEE), external ear canal, and the nasopharynx was carried out on 458 patients with otitis media with effusion. Staphylococcus epidermidis was the most common bacteria in MEE, even after excluding the contaminants from the external ear canal, which had the same value of minimal inhibitory concentration as the paired MEE. The bacterial agreement of S epidermidis between MEE and the nasopharynx was extremely rare in contrast with Haemophilus influenzae, Streptococcus pneumoniae, and Branhamella catarrhalis, although the organism was also frequently isolated from the nasopharynx. Staphylococcus aureus, having the same minimal inhibitory concentration as that in the nasopharynx, was more frequently found in MEE than S epidermidis. The results suggest that S epidermidis found in MEE is not a pathogen, but rather a contaminant in many instances. Staphylococcus aureus seems to be a causative agent in otitis media with effusion. otitis media with effusion (OME) had in general been assumed to be sterile until Senturia et al1 were able to identify bacteria by means of smears and cultures of middle ear effusion (MEE) from children with OME. Since then, many investiga¬ tors26 have reported on the presence of a high percentage of bacteria in MEEs.Haemophilus influenzae, Streptococcus pneumoniae, and Branhamella catarrhalis are frequently found in MEEs, and are commonly considered pathogens of OME.5-6 How¬ ever, whether Staphylococcus aureus and Staphylococcus epidermidis, also frequently present in MEEs, are caus¬ ative agents in OME is still controver¬ sial. Senturia et al1 found that the most common bacterial species in MEE was S epidermidis, and stated that bacteria from the external ear canal had contaminated the effusions.Riding et al4 considered S aureus and S epidermidis as "doubtful patho¬ gens," because these organisms were frequently found in both the external ear canal and the middle ear. On the other hand, Bernstein et al' demon¬ strated the presence of antibodycoated coagulase-negative staphylo¬ cocci in various types of effusions.They suggested that this organism may not always be a contaminant, but that it may play a role in the patho¬ genesis. Feigin et al8 were able to isolate S epidermidis in pure culture from purulent MEE in a few children with acute otitis media.To clarify this problem, detailed bactériologie analysis of OME is nec¬ essary. Bernstein et al9 determined the biochemical profiles and patterns of antibiotic susceptibility of coagulase-negative staphylococci isolated from MEEs, ear canals, and adenoid tissues. In this study, the external ear canal was thoroughly sterilized, and further bacterial identification was attempted by determining the mini¬ mal inhibitory concentration (MIC) of several antimicrobial agents against the bacterial isolates from patients with OME. The findings of the orga¬ nisms from the external ear canal, MEE, and the nasopharynx were investigated in detail, and the possi¬ bility of S epidermidis and S aureus as causa...