Yersinia enterocolitica and Yersinia pseudotuberculosis are current sources of pathogenic strains in humans and animals. Yersiniae infections occur throughout the world, but are most prevalent in regions with moderate and subtropical climates. In Australia, Central Europe and North America, cases of human infections with Yersinia enterocolitica now rank in third place. The food-processing industry may influence the epidemiological situation in different ways. Effluents which contaminate the environment may originate from slaughterhouses; e.g. from sewage contaminated with faeces from the lairage or contaminated effluents from the actual slaughter areas. The carcasses may serve as carriers of the organisms to the food-processing plants where they eventually contaminate the processed foods. Rodents and pests may also be carriers. Pathogenic Y. enterocolitica and Y. pseudotuberculosis strains mainly occur in swine and pork. The ability to multiply under refrigeration and in vacuum-packaged products means that pathogenic Y. enterocolitica can cause foodborne diseases. If a plant harbours any pathogenic Yersiniae, transfer of the contaminant to the sewage is possible. Although pathogenic Yersiniae from infected animals can survive in sewage and in surface waters, the role of properly treated sewage in the transmission of yersiniosis seems to be of minor importance. If the recommendations for modern slaughter techniques are properly followed, the spread of pathogens in the slaughterhouses and, subsequently, into other food-processing plants can be minimised.