Merino sheep vaccinated with either wholeBucteroides nodosusorganisms, a crude surface antigen preparation or highly purified pili (>99% homogeneity) in oil adjuvant, developed significant resistance to artificial footrot infection when compared with unvaccinated control sheep inoculated with saline-in-oil emulsion (Freund's incomplete adjuvant) alone. The pili-vaccinated sheep generally had higher K-agglutinating antibody titres than sheep vaccinated with wholeB. nodosus. These results confirmed the role ofB. nodosuspilus protein both as a protective antigen and the K-agglutinogen.