Tympanocentesis was performed in 50 patients with chronic otitis media. Pus was cultured aerobically and anaerobically. Aerobes only were isolated from 21 patients, 3 had only anaerobes (peptococcus sp.) and 26 had both aerobes and anaerobes. There were 68 aerobic isolates. Pseudomonas aeruginosa was recovered in 36 (72%). Other aerobes commonly recovered included proteus sp. and Staphylococcus aureus. There were 48 anaerobes isolated. Anaerobic gram positive cocci were isolated in 24 instances. Sixteen Bacteriodes sp. were recovered, including 7 B. fragilis and 6 B. melaninogenicus. The patients were divided into two groups according to their antimicrobial therapy: 28 received carbenicillin and 22 clindamycin. An aminoglycoside was added when aerobic enteric gram negative rods were present in significantly high numbers in the culture. There was good to excellent response to therapy in more than half of the patients and in 12% there was a remission from symptoms for up to one year. Thirty-six percent of the patients had no response to therapy. There were no statistical differences in response to therapy in the two groups treated. Antimicrobial therapy directed against aerobic and anaerobic isolates from chronic otitis media had a high success rate in complete eradication of the infection.