There exists no real controversy about the role of aerobic bacteria in acute sinusitis and in acute otitis media. The "infernal trio" Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis are by far the most common pathogens in these acute infections. On the contrary, there is still much debate about the normal flora of the paranasal sinuses and the middle ear, although there are some reports of the presence of anaerobes and aerobes in the majority of the normal paranasal sinuses. In chronic sinusitis bacteriological cultures show a greater variation than those in acute sinusitis. Nonetheless, it is demonstrated in most studies that besides the "infernal trio" additional bacteria are present, including anaerobes and gram negative bacteria. In otitis media with effusion (OME) we find the same bacteria as in acute otitis media (AOM) and a pathologic flora in the nasopharynx seems to be important for both AOM and OME. In chronic otitis cultures are nearly always positive and reveal Pseudomonas species, Klebsiella pneumoniae, Staphylococcus aureus, Proteus species and anaerobes.