In a single blind, randomized study, 46 patients with acute external otitis were treated with either oxytetracycline/hydrocortisone with polymyxin B (TPB) or hydrocortisone-17-alpha-butyrate eardrops for 7 days. Pseudomonas pyocyanea, Staphylococcus epidermidis and Staph. aureus were the microorganisms most frequently found in the ear canal. Fungi were not found in any culture. The overall cure rate was 80%. No significant difference in therapeutic efficacy was noted between the preparations except regarding Staph. aureus, which was cultured from 17% of the patients. Although the butyrate solution did not contain any antibiotic supplement, it seemed to be more effective than TPB in treating the staphylococcal infections. These findings suggest that such other factors as the hydrogen ion concentration, the steroid potency or the vehicle per se are of importance for the successful treatment of acute external otitis.