Viruses--both alone and in combination with bacteria--have been shown to be a cause of acute otitis media (AOM). Moreover, the presence of virus in middle ear fluid (MEF) interferes with the bacteriologic response to antibiotic treatment in AOM. We studied various factors related to the eradication of bacteria from the MEF of infants and children who had AOM associated with a combination of bacteria and viruses. Of 622 cases of AOM diagnosed and treated between 1985 and 1991, 71 were due to such a combination. Bacteria were eradicated from MEF by 2-4 days of antibiotic treatment in 50 (70%) of these 71 cases; in the remaining 21 cases, the originally identified bacteria persisted or a new pathogenic bacterial species was detected after such treatment. These two groups of cases were compared with respect to the patients' age, sex, race, history of recurrent AOM, duration of respiratory symptoms, and compliance; the type of antibiotic treatment administered; the type of pathogenic bacteria and viruses identified in MEF; the presence of single or multiple pathogens; and the laterality of the disease. The only difference noted was in the type(s) of virus found in MEF. The presence of rhinovirus was associated with a higher rate of bacteriologic failure than was that of respiratory syncytial virus, parainfluenza virus, influenza virus, or other viruses. Our data suggest that the bacteriologic response to antibiotic treatment in bacterial-viral AOM may depend in part on the type(s) of virus present in MEF.