Aspirates from 48 chronically inflamed maxillary sinuses from patients who had nasal polyposis were processed for aerobic and anaerobic bacteria. Bacterial growth was present in 46 (96%) specimens. Aerobic or facultative bacteria were present in 6 (13%) specimens, anaerobic bacteria alone in 18 (39%), and mixed aerobic and anaerobic bacteria in 22 (48%). There were 110 bacterial isolates (2.4 per specimen). Thirty-nine of the isolates were aerobic or facultative organisms (0.85 per specimen). The predominant aerobic or facultative organisms were: Staphylococcus aureus, microaerophilic streptococci, Haemophilus influenzae and Moraxella catarrhalis. Seventy-one anaerobes were isolated (11.5 per specimen), Peptostreptococcus spp., Prevotella spp., Porphyromonas asaccharolytica and Fusobacterium spp. being predominant. These findings illustrate for the first time the presence of polymicrobial aerobic-anaerobic flora in patients with chronic maxillary sinusitis who had nasal polyposis.