It has been reported that intranasal immunization can induce mucosal immune responses. However, the efficacy of intranasal immunization on otitis media caused by non-typeable Haemophilus influenzae (NTHi) is not yet elucidated. Mice were intranasally, orally, intratracheally or intraperitoneally immunized with outer membrane protein (OMP) isolated from NTHi, and antigen-specific immune responses were determined by enzyme-linked immunosorbent assay (ELISA) and enzyme-linked immuno-spot assay (ELISPOT). Cytokine production from splenic CD4+ T cells was examined by ELISA. Following the immunization, the clearance of NTHi from the nasal and nasopharyngeal cavity was examined. OMP-specific IgA antibody titers in nasal washes and the numbers of specific IgA-producing cells in nasal passages were significantly increased in intranasally immunized mice. Cytokine analysis showed that interferon-γ (IFN-γ) and interleukins IL-6 and IL-10 were predominantly produced from CD4+ T cells. The clearance of NTHi was significantly enhanced in the intranasal immunization group. Intranasal immunization is an effective vaccination regimen for the induction of OMP-specific mucosal immune responses. Copyright (C) 1999 Elsevier Science Ireland Ltd.