Many septicaemic Escherichia coli strains harbour CoIV virulence plasmids. This paper describes pO78V, a conjugative CoIV plasmid from an avian pathogenic E. coli strain that encodes type IV pili in addition to other virulence-related genes and tetracycline resistance. Plasmid location of type IV pili genes was demonstrated using Southern hybridization and expression of the pili was demonstrated using RT-PCR and phage sensitivity assays. This is a first report of a CoIV plasmid encoding type IV pili. Plasmid pO78V is a mosaic plasmid containing replicons and other genes typical to both Incl1 and IncFII groups. As type IV pili of Gram-negative bacteria are involved in several stages of infection, their presence on a ColV virulence plasmid could expand the repertoire of pathogenesis-related genes.