Two Bordetella pertussis antigen preparations, outer membrane protein (OMP) and filamentous haemagglutinin (FHA), and a standard vaccine were used to immunize rabbits, and the effects on nasopharyngeal colonization by the organism were determined. Antibodies were measured in serum and in nasal washes by ELISA before and after challenge of the rabbits with 106 bacteria of strain M2. Recoveries of B. pertussis in nasal washes were used to assess colonization, which in controls persisted for at least 65 days. Some rabbits of all the immunized groups showed enhanced clearance, but there was no correlation between the elimination of B. pertussis and serum antibodies to OMP, FHA, lipopolysaccharide, lymphocytosis-promoting factor or agglutinogen 3. In contrast, nasal IgA antibody to FHA showed significant inverse correlation with bacterial persistence. Such antibody was induced by the OMP preparation as well as by FHA, but to different extents depending on the immunization schedule and adjuvant used.