During 1979 a large-scale study of fecal samples obtained from patients with acute intestinal infections was carried out with the aim of establishing the presence of Yersinia. As a result, 9 Y. enterocolitica strains and 7 Y. pseudotuberculosis strains were isolated. Y. enterocolitica were classified with serovars O8, O3, and O5B and with biovars 2, 3, and 4; Y. pseudotuberculosis were classified with serovars 1 and 3. The isolation of Yersinia facilitated the identification of the etiological structure of acute intestinal infections.