The 16S rRNA genes from virulent (AB) and benign (B) biotype strains of Fusobacterium necrophorum, the causative agent of ovine foot abscess, were cloned and sequenced. Notwithstanding the distinct phenotypic differences between the AB and B biotypes, a phylogenetic analysis in which the 16S rRNA gene sequences were used revealed the close relationship of these taxa. Comparison of the virulent and benign biotypes of F. necrophorum may therefore be a legitimate way to identify key virulence factors useful in vaccine development.