SUMMARYThe properties of 48 cultures identified asYersiniaenterocoliticaorY. enterocoliticalike organisms, includingY. frederiksenii,Y. intermediaandY. kristensenii, were examined. Of these, 39 were isolated from flieces of apparently healthy pigs, five from healthy cattle, one from an aborted bovine fetus, one from an aborted lamb and one from a lamb suffering from acute enteritis.Most isolates from healthy animals were ofY. enterocoliticabiotype 1 orY. intermediaand belonged to O serogroups not usually associated with disease in man or animals.The isolates from abortion or enteritis cases were ofY. enterocoliticabiotypes 3, 4 and 5 and belonged to the pathogenic serogroups 0:5b and 0:2a, 2b, 3. No organisms of serogroup 0:9 were found.