A batch of 186 strains belonging to the families Enterobacteriaceae or Vibrionaceae has been studied by determination, for each strain, of the "versatility" towards 146 organic substrates tested as sole source of carbon and energy. This study allowed to work out a classification of these strains into the 32 classes which have been previously described. In the present paper the nutritional characters of these classes are reported. On the basis of these characters, the 32 classes may be regrouped into 7 groups, namely: (1.1) "Escherichia-Salmonella-Citrobacter", (1.2) "dystrophic Klebsielleae", (1.3) "eutrophic Klebsielleae", (2.1) "Shigella", (2.2) "Proteus", (2.3) "Aeromonas-Vibrio", (2.4) "Edwardsiella tarda-Aeromonas salmonicida-Plesiomonas shigelloides". Only 4 strains (about 2 percent) happened misclassified in this study where the taxa were assembled exclusively by means of nutritional characters. The number and the type of the substrates which can be used in each group are reported, as well as the nutritional characters which are possibly useful to differential diagnosis. The taxonomic considerations which may be deduced from this study are discussed.