A 40-yr-old buddhist monk was admitted to the hospital with abdominal pain, fever, and confusion. He had a history of drinking untreated mountain spring water in his temple, and experienced the above symptoms for several days before admission. In past medical history, he had suffered from hepatic cirrhosis. Yersinia pseudotuberculosis was isolated from his blood and ascitic fluid. The mountain spring water that he had ingested was cultivated and Y. pseudotuberculosis was also isolated. For identification of pathogenic Y. pseudotuberculosis, each isolate from the three sources (blood, ascitic fluid, and drinking water) was also analysed for the inv gene for Y. pseudotuberculosis and the virF gene for virulent plasmid by PCR. All strains were positive for both the virF and the inv genes and also positive for autoagglutination test. For relationship study, each isolate from the three sources was also analysed with serotyping and restriction endonuclease analysis of virulence plasmid DNA (REAP) using BamHI. All belonged to the serotype 4b and REAP pattern D. Thus, all these findings supported that the mountain spring water was the source of the Y. pseudotuberculosis infection in this case.