Over a 22-month period, all 5075 faecal specimens received by the microbiology laboratory of the Mater Misericordiae Public Hospital, Brisbane, were screened for the presence of Yersinia enterocolitica by culturing on cefsulodinirgasan-novobiocin agar medium. Y. enterocolitica was isolated from 37 patients (0.7% of all specimens). Ten patients were 10 years of age or older, and presented predominantly with pain in the abdomen; of these, five underwent an appendicectomy. Mesenteric adenitis was diagnosed histologically in three patients and Y. enterocolitica was isolated from a lymph-node biopsy specimen in one of these. The other 27 patients were under 5 years of age, and presented predominantly with diarrhoea of 24 hours' to six weeks' duration. In seven cases, another recognized faecal pathogen was also isolated. The isolation rate of Y. enterocolitica was one-quarter that of Salmonella and seven times that of Shigella.