163 clinically normal slaughtered pigs were examined for the presence of Yersinia enterocolitica and Yersinia pseudotuberculosis. The following results were obtained: Yersinia enterocolitica was isolated from the tonsils in twenty-two cases, Yersinia pseudotuberculosis being found to be present in the tonsils in seven cases, Yersinia enterolitica was isolated from the liver in one case and from the caecal contents in eight cases, and Yersinia pseudotuberculosis was isolated from the caecal contents in three cases. These bacteria were not isolated from the mesenteric lymph nodes and muscle tissues. All sixty samples of minced raw pork which were examined, were also negative for these micro-organisms. Almost all strains isolated were of the same serotypes as those isolated from man in the Netherlands. The findings did not suggest that ingestion of raw pork might involve a risk of human yersiniasis. It is doubted, however, whether the methods of isolation were sufficiently selective.