Due to local and systemic side-effects, the currently used, highly effective, whole-cell pertussis vaccines (WCVs) will be replaced by acellular vaccines (ACVs) in some countries. These ACVs contain detoxified pertussis toxin, either alone or in combination with the filamentous haemagglutinin, pertactin and fimbriae. Ongoing clinical trials show that ACVs are clearly less reactogenic than WCVs and that ACVs comprised of three to five proteins are highly efficacious in inducing protection against Bordetella pertussis infections. An important unresolved question is, what the effect will be of the switch from WCVs to ACVs on the incidence of Bordetella parapertussis infections, the second causative agent of pertussis. A comparison of the efficacy of WCVs and ACVs against B. parapertussis infection is required to answer this question. We show that the Dutch WCV, although prepared from B. pertussis strains, protects against B. parapertussis infection in a murine respiratory model, although less efficiently than against B. pertussis infection. It was shown previously that the ACV components pertussis toxin, FHA and pertactin did not protect against B. parapertussis infection in a murine respiratory model. We have investigated the efficacy of two other ACV components, B. pertussis serotype-2 and -3 fimbriae against B. parapertussis infection in the murine model. The B. pertussis fimbriae protected mice against B. parapertussis infection although less efficiently than against B. pertussis infection. This result indicates that B. pertussis and B. parapertussis fimbriae are antigenically distinct. B. pertussis fimbriae were found to be as efficacious as the WCV against B. pertussis infection. Our results are discussed in the light of the switch from WCVs to ACVs.