During the period of 6 months from November 1980 to April 1981, five strains of Yersinia enterocolitica were isolated from fecal materials of adult patients with acute enterocolitis. The followings are summary of our experience on the strains isolated. 1) All of the organisms were isolated from the S-S agar plates after inoculation in 18 hours' selenite F broth. The cultural difficulty was due to both very slow growing rate and sensitivity to the temperature of the organisms. 2) The isolates revealed cultural and biochemical characteristics on the conventional and API-2OE methods. Three isolates were indole negative at room temperature, belonging to Wauter's biotype 3, and two were indole positive, belonging to the biotype 2. 3) The isolates were all susceptible to amik1acin, chloramphenicol, gentamicin, kanamycin, streptomycin, tetracyclin, and three strains of biotype 3 showed resistance to cephalothin, ampicillin and carbenicillin, while biotype 2 strains were resistant to cephalothin. 4) The five patients of Yersiniosis were well controlled by ampicillin, lianamycin and septrin, in single or in combination chemotherapy.