Study of biochemical properties of 421 strains of enterobacteria permitted to refer them to the following taxonomic groups of which E. coli constituted 83,4 +/- 3.6%, Enterobactercloacae--97 +/- 3.0%, Klebsiella 4.0 +/- 2.0%. Enterobacter aerogenes, Enterobacter hafnia, Citrobacter, Proteus rettgeri, Proteus vulgaris were revealed in individual cases (0.2-1.0%). As a result of serological typing there were revealed 105 serological types of Escherichia differing by 55 O-antigen variants, 26 H-antigen variants, and the presence or absence of K-antigen. The following groups occurred most frequently-01, 02, 04, 06, 08, 09, 015, 016, 017, 018, 025, 028, and 075. There were also revealed new 0154 and 0155 groups. In 30.9 + 5,3% of cases Escherichia did not belong to the known 157 O-groups; among them 87.1 +7,2% of the strains had H-antigens which could not be referred to any of the known variants according to the international designation.