A study was made of 239 strains of enteropathogenic escherichia 0151:K-- isolated in various regions of the USSR from patients with the clinical diagnosis of dysentery, gastroenteritis, intestinal coli-infection: a standard strain of the international collection of escherichia belonging to the given serological group was also studied. There was shown an increase in the role of these microorganisms among the enteropathogenic escherichia recorded at the territory of the USSR; they occupied the third place by the frequency of isolation after the serological group 0124:K72 and 0111:K58. There was established a common nature of the enzymatic characteristics of escherichia 0151:K--with shigellae by the absence of lactose, sucrose, inosite, adonite fermentation, the presence of gasless, immobile variants containing no lysin decarboxylase, and a possibility of rapid differentiation from shigellae in the use of acetate medium. Among the escherichia 0151:K--there was revealed the presence of 5 biotypes by the capacity to gas-formation in glucose, arabinose, sorbit, dulcit fermentation, and decarboxylation of lysin and ornithin; three biotypes are described for the first time. Industrial issue of the agglutinating serum 0151:K--is necessary to provide the diagnosis of these microorganisms at the territory of the USSR.