The thermogenesis of 17 strains belonging to 12 species of the Enterobacteriaceae family was measured at 30 °C with an ampoule microcalorimeter. It was analyzed qualitatively (aspect of profiles) and quantitatively (total heat evolved, thermogenesis duration, maximum thermal power). The value of these criteria is discussed with respect to their discriminating value in the classification of bacteria. The information obtained may concur with the identification of species; it gives ground to reconsider actual phenotypes and genotypes and taxonomy generally. [Journal translation]