Whole killed meningococci (Nm) and pertussis bacteria (Bp) were tested for mucosal immunogenicity and as mucosal adjuvants for an inactivated influenza virus vaccine given intranasally to unanaesthetized mice. Virus was given alone, or simply mixed with one of the bacterial preparations, in four doses at weekly intervals. The virus alone induced low but significant increases of influenza-specific IgG antibodies in serum measured by ELISA, whereas IgA responses in serum and saliva were insignificant compared to non-immunized controls. With Bp or Nm admixed, serum IgG and IgA and salivary IgA responses to the influenza virus were substantially augmented (P<0.005). However, this adjuvant effect of the bacterial preparations was not significant for responses in the intestine as measured by antibodies in faeces. Antibody responses to Bp itself, but not to Nm, were inhibited by the admixture of the virus vaccine. Moreover, the pertussis preparation induced salivary antibodies which cross-reacted with Nm. Whole-cell bacteria with inherent strong mucosal immunogenicity may also possess mucosal adjuvanticity for admixed particulate antigens which are weakly immunogenic by the nasal route.