The sensitivity of some phenotypes of Yersinia to 7 phages isolated from lysogenic strains of Y. frederiksenii, Y. kristensenii and Y. intermedia was investigated. Among the strains involved in human pathology in Europe, Y. enterocolitica serovar O:3 was sensitive to 7 phages tested, while serovar O:9 was sensitive to all but one phage. Strains isolated from the environment, considered as non-pathogenic, were much less susceptible to the 7 phages. Based on these results, a new phage typing system which differentiates Y. enterocolitica O:3 and O:9 from the other Yersinia is proposed.