In a novel adherence model using tracheal rings removed from Papio anubis, we have demonstrated a functional role for the fimbriae of Bordetella pertussis. When compared to wild-type strains, B. pertussis mutants specifically deficient in fimbriae adhered less well to the tracheal rings but better to Vero (Green monkey kidney) cells. In contrast, mutants deficient in filamentous haemagglutinin (FHA) production had reduced adherence to both Vero cells and the tracheal rings. These observations indicate that the fimbriae of B. pertussis, like those of many other bacterial pathogens, may play an important role in the initial stages of colonisation.