The analysis of the chromatograms of methyl esters of fatty acids in bacterial strains of the tribe Klebsielleae showed the heterogeneity of the fatty acid composition of bacteria belonging to the genera Klebsiella, Enterobacter, Hafnia and Serratia. The bacteria of this tribe could be subdivided into 5 provisory groups in accordance with the composition and profile of their fatty acids. Group I comprised K. pneumoniae K1, K. ozaenae and K. rhinoscleromatis strains forming a separate group characterized by the absence of cyclopropane fatty acids; group II comprised K. pneumoniae strains of other capsular serovars (K2, K8, K11, K13, K41, K47), as well as K. aerogenes and K. oxytoca strains. The fatty acid composition of the strains of group III, comprising E. aerogenes and E. cloacae, was similar to that of E. coli O1; only among the fatty acids of these bacteria acid C20:0 could be detected. H. alvei strains were included into group IV; their fatty acid profiles were similar to those of the genus Enterobacter, but had a higher content of acids C15:0 and C18:0. S. marcescens strains were similar to the strains of group II in their fatty acid composition, but considerably differed from the latter by a higher content of hexadecanoate (C16:0) and a lower level of C18:1; for this reason they were regarded as provisory group V.