Helicobacter pullorum has been isolated from the feces and livers of poultry and is associated with human gastroenteritis. Discrimination of this organism from other enterohepatic Helicobacter species and Campylobacter species has proven difficult. H. pullorum from both avian and human clinical sources has DNA sequence homology and cytotoxic activity that represent a new member of the cytolethal distending toxin (CDT) family of bacterial toxins. CDT is a potential virulence factor in H. pullorum that may serve as a distinguishing phenotype and aid in identification of this organism in veterinary and human clinical samples.