The classification of 175 strains related to the genus Enterobacter has been carried out by numerical procedure, with usual biochemical and nutritional characters as shown by the utilization of substrates tested as sole sources of carbon and energy. The taxonomic position of the strains is discussed in relation to the species E. cloacae, E. hafniae, E. aerogenes, E. agglomerans and Serratia liquefaciens. By the system of data analysis used (hierarchical agregation method) five principal classes can be defined. The individualization of new classes closely bound to the diverse origins of the strains examined (human, soil, aquatic).