A murine model for pulmonary clearance of Moraxella catarrhalis was used to determine whether immunization could enhance clearance of this organism from the lungs. Animals actively immunized with outer membrane vesicles of M. catarrhalis cleared an endobronchial challenge with the homologous strain more quickly than did sham-immunized control animals. Western blot analysis of both this immune mouse serum and rabbit antiserum raised against outer membrane vesicles of M. catarrhalis indicated that antibodies were present to both outer membrane protein and lipooligosaccharide antigens. Passive immunization of mice with the immune rabbit serum resulted in enhanced pulmonary clearance of both homologous and heterologous strains of M. catarrhalis, indicating the involvement of serum antibody in this clearance process and the existence of conserved surface antigens in the two different M. catarrhalis strains. These results suggest that this model system may be useful for the identification of vaccine candidates among the surface antigens of M. catarrhalis.