Infective animal sources and persons in contact with animals were investigated for Yersinia enteroclotica. The 68 isolates from 3115 animals belonged to four serogroups. The most frequent was serogroup O3 (62 strains) found mainly in pigs (41 strains). The same serogroup was isolated from dogs (9 strains), cats (6 strains) and from other animals (6 strains). A total of 556 animals living in the Budapest Zoo were examined. Y. enterocolitica was isolated from the faecal specimens of one chimpanzee and one gibbon. Using the Widal-type agglutination, out of sera of 877 persons in contact with animals, 4.56% were positive with antigens O3 and O9, compared to 0.33% in healthy controls. The study indicates that beside the occasional role of other animal species, pigs should be regarded as the main source of human enteric yersinosis.