The aim of this study was to compare the efficacy and safety of a topical suspension of bacterial antigens for the management of chronic suppurative otitis media (CSOM). Two-hundred ten patients with CSOM were enrolled in this study. The patients were divided into two numerically equal groups and randomized to receive a topical suspension of bacterial antigens, Lantigen B (group A), or placebo (group B), according to the following protocol: 5 drops thrice a day for 12 consecutive weeks in the external acoustic duct. The topical suspension of bacterial antigens and placebo were administered by identical, anonymous dispensers in order to maintain double-blind conditions. Before, at the end and 3 months, and after the end of the treatment, all patients who entered in the study underwent pure tone audiometry, microscopic examination of ears, microbiological examination of the ear swab, aural suctioning and subjective assessment of symptoms by visual analog scale. In group A, we saw a statistically significant improvement in the different items measured. A topical suspension of bacterial antigens was significantly more effective than placebo in the treatment of CSOM.