Enterotoxigenic strains of Vibrio cholerae O-1 biotype eltor, isolated from three sporadic cases of cholera in Nagoya in 1989 and an outbreak of cholera in Nagoya in 1989 were analyzed for their similarities. All isolates of V. cholerae O-1 were indistinguishable in bacteriophage types, serovars, biovars and drug resistance patterns. Because the epidemiological investigation based on a primary structure of chromosomal DNA is more reliable, we isolated chromosomal DNA from these isolates and compared electrophoretic patterns of restriction endonuclease-digested DNA fragments. Furthermore, Southern hybridization of the cholera toxin gene was performed. Since no difference among six strains in these sporadic was observed, it was strongly suggested that both the independent cases and the outbreak of cholera were caused by the same strain.