Eight bacterial strains were examined whether they have phoP/phoQ genes which were known to be involved in the intracellular survival of Salmonella typhimurium. The phoP/phoQ operon were known to sense the stimuli of the genes involved in the adaptation of the environment. Using 514-basepairs EcoRV DNA fragment of phoP region of Salmonella typhimurium as a probe, dot blot hybridization were performed. Chromosomal DNAs of Klebsiella pneumoniae, Pseudomonas aeruginosa, Serratia marscescens, Enterobacter cloacae, Salmonella typhimurium, Escherichia coli, Shigella dysenteriae, and Listeria monocytogenes were examined by DNA hybridization assay. Against our expectation, intracellular pathogen, L. monocytogenes, did not have similar DNA sequences to phoP/phoQ of S. typhimurium, while E. coli, S. dysenteriae, and E. cloacae showed the positive signal even though they were not intracellular pathogens. This result suggested that the phoP/PhoQ operon was absent in intracellular pathogenic bacterias other than S. typhimurium. Rather it was found in phylogenetically closer bacterias to S. typhimurium, which were not able to survive in intracellular environment. Some different mechanism, which is not dependent on phoP/PhoQ operon, could be involved in the intracelluar survival of L. monocytogenes.