• Aspiration of the exudate through open perforation was performed in 48 children with chronic suppurative otitis media. Eighty-two aerobic and 93 anaerobic isolates were recovered. Aerobic bacteria only were involved in 22 patients (46%), and anaerobic organisms only were involved in five patients (10%). Mixed aerobic and anaerobic isolates were recovered from 21 patients (44%). The most common bacteria isolated were Bacteroides melaninogenicus group (40% of patients), Pseudomonas aeruginosa (29%), Klebsiella pneumoniae (10%), and Staphylococcus aureus (10%). There were 50 β-lactamase–producing organisms (26 anaerobes and 24 aerobes) recovered from 33 patients (69%). Forty-four of these bacteria were isolated from the 37 patients recently treated with a penicillin. These included all ten isolates of S aureus and Bacteroides fragilis group, 11 of 19 of B melaninogenicus group, five of the 14 P aeruginosa, three of ten K pneumoniae, three of six of Bacteroides oralis, four of six of Haemophilus influenzae, two of three of Staphylococcus epidermidis, and two of four of Branhamella catarrhalis. The β-lactamase–producing organisms have a possible role in the failure of penicillin therapy.