This study was designed to determine the middle ear bacterial pathogens, the frequency of serum immunoglobulin deficiency and the efficacy of medical management in patients with chronic suppurative otitis media without cholesteatoma. This was an open noncomparative clinical trial performed at the National Children's Hospital, San Jose, Costa Rica, and included 186 patients older than 2 months of age with a confirmed diagnosis of chronic suppurative otitis media without cholesteatoma. Middle ear cultures and serum for immunoglobulin determinations were obtained on admission. The first 40 patients were treated only with ceftazidime and from patient 41 and up, if a Grampositive organism was cultured, oxacillin was added to (for combined infection) or replaced ceftazidime. Parenteral antibiotics and suction twice daily were continued until three days after the middle ear became dry. Trimethropimsulfamethoxazole prophylaxis was administered during the follow-up period. Middle ear bacterial cultures were positive in 166 patients.Pseudomonassp. (35.6%), enteric Gram-negative organisms (28.7%) and Gram-positive cocci (26%) were the most common organisms. Immunoglobulin determinations were below normal in 3 of 69 (4.3%) evaluable patients. Dryness of the ear was achieved in 174 patients (93.5%) including 130 of 139 patients treated with ceftazidime, 28 of 28 patients treated with oxacillin and 14 of 14 patients treated with ceftazidime and oxacillin. Recurrent otorrhea developed in 39 (23.4%) patients. Twice-daily canal aspiration and parenteral ceftazidime for Gram-negative organisms and/or oxacillin for Gram-positive bacteria for 3 days after dryness of the middle ear followed by prophylactic oral antimicrobials are effective for treatment of most chronic suppurative otitis media without cholesteatoma patients.