A recombinant plasmid pMM-CTII containing cholera toxin (CT) gene was constructed in vitro. The specific DNA fragment from CT gene was obtained by XbaI and EcoRI double digestion of pMM-CTII follow by agarose gel electrophoresis and then labelled with .alpha.32P using nick translation technique. The labelled CT probe showed positive hybridization results with classical V. cholerae O1 group and Eltor toxigenic strains and negative hybridization results with O1 group nontoxigenic strains. We also identified 52 epidemic and 50 resistant strains of V. cholerae Eltor which were typed by bacteriophages and isolated from clinical specimens and environment. The detection ratio of toxigenic strains were 92% and 16% respectively. It shows that CT gene analysis is more accordance and confident than bacteriophage classification method.