Three outbreaks of Yersinia pseudotuberculosis infection during 1982 to 1984 in Okayama Prefecture, Japan are described. In outbreak A, Yersinia pseudotuberculosis a causal organism was detected in 16 patients (serotype 5A). The latent period of the infection was 2 to 20 days estimating, from time of ingesting food suspected of being contaminated and onset of the illness. Outbreak B and C occurred in remote mountain areas. In outbreak B, Yersinia pseudotuberculosis bacilli were detected in the feces of 35 out of 276 people (serotype 4B in 34 stools, 2C and 4B in one stool). In outbreak C, 12 children became sick; one of the 4 patients whose stools were examined, showed an organism belonging to serotype 4B. The inhabitants in the area of outbreak B and C took unchlorinated mountain stream and well water for drinking. After the outbreak B and C, we examined water and wild animals fecea in these areas for the bacilli. As a result, they were detected in 3 out of 51 water samples (serotype 4A in one, 6 in 2 samples) and 2 out of 57 wild animal fecal samples (serotype 2C in 2 samples) in B area, and 4 out of 33 water samples (serotype 4A in 2, 4B in 2 samples) in C area.