M.I.S.-Enterobacteriaceae is a new kit for identifying Enterobacteriaceae using a microplate consisting of 21 biochemical characters with automated reading and interpretation. The validity of this method was studied by the identification of 350 strains of enterobacteria belonging to 44 species and comparison with the classical method of identification in test-tubes. Results showed a diagnosis accuracy of 96 p. cent at the species level and 97.7 p. cent at the genus level. Diagnosis accuracy reached 100 p. cent for those bacterial species isolated routinely: Proteus, Providencia, Morganella, Klebsiella, Enterobacter. Accuracy was 97 p. cent for E. coli, 95 p. cent for Serratia marcescens and 94 p. cent for C. freundii. For several less frequently isolated species such as Salmonella, Hafnia, Shigella and Yersinia, diagnosis accuracy was 100 p. cent. This identification system for enterobacteria can however also be used for identification of Aeromonas genus and for Pseudomonas maltophilia and Acinetobacter baumannii non fermenting Gram-negative bacilli with oxidase negative reaction.