Objective:To evaluate the effectiveness of prophylactic polymyxin B sulfate-neomycin sulfate-hydrocortisone drops in decreasing the incidence of posttympanostomy otorrhea.Design:Prospective randomized controlled study.Setting:University referral center.Patients:Three hundred patients undergoing tympanostomy tube placement (including those undergoing tonsillectomy, adenoidectomy, or both) were randomized into three groups.Intervention:The use of polymyxin B-neomycin-hydrocortisone drops. Patients in group 1 received no antibiotic drops; group 2, a single dose intraoperatively, and group 3, an intraoperative dose followed by a 5-day course.Main Outcome Measure:Posttympanostomy otorrhea.Results:A statistically significant decrease was observed in the incidence of posttympanostomy otorrhea between the control (16.4%) and treatment groups (group 2, 8.3%; group 3, 8.1%) (P=.011). A single dose of antibiotics was effective when patients' middle ears were dry or had serous effusions. A 5-day course was indicated for those whose ears had mucoid or purulent contents.Conclusions:Antibiotic ear drops are indicated in all patients. A single dose is as effective as a 5-day course, but our data support a longer course in certain subgroups.(Arch Otolaryngol Head Neck Surg. 1995;121:445-448)