Data pertaining to 1,219 cultures of Yersinia enterocolitica isolated in Canada are summarized. Of the 977 cultures isolated from humans, Y. enterocolitica serotype 0:3, biotype 4, phage type IXb was the most predominant type in Ontario, Quebec and the four Eastern Provinces. In the Western Provinces the predominant strains were indol-positive, serotypes 0:8; 5,27 and 4,32. Most of the 242 cultures of nonhuman origin, except those isolated from swine and a few isolated from wild animals, were indol-positive, biochemically atypical and serologically nontypable or belonging to different serotypes which have seldom been found in human infections.