The utility of a simple biotyping scheme to differentiate pathogenic and non-pathogenic strains of Yersinia enterocolitica was determined for 79 patients who were admitted to or attended a reference children's hospital in western Canada. Biotyping defined predominantly two subsets of Y enterocolitica. 'Pathogenic' strains were more likely to have been obtained from younger patients (mean age 61.9 months) who experienced an acute gastrointestinal illness that was occasionally associated with bloody diarrhoea or a surgical procedure. Growth of Y enterocolitica from selective solid bacteriological growth media were often in the moderate to heavy range (82.0%). In contrast, 'non-pathogenic' strains were more often obtained from older patients (mean 116.0 months) who were already recognised to have suffered from a chronic illness and who were likely to have been admitted to hospital. Moderate to heavy growth of bacterium in stool specimens were infrequently (17.4%) obtained from the latter patients. The use of a simple biotyping scheme for the differentiation of Y enterocolitica strains has the potential to improve patient care.