An ecological and molecular-epidemiological study of Vibrio cholerae in some aquatic environments of Okayama was carried out. The strains of non-O1/non-O139 were isolated frequently, and unconventional O1 strains were rarely observed. These non-O1/non-O139 strains did not have ctxA, the gene of choleratoxin, the major pathogenic factor of epidemic cholera, but possessed hlyA, a gene encoding hemolysin thought to be a pathogenic factor for sporadic diarrhea or food poisoning. Furthermore these strains also had toxR, a gene controlling the pathogenic island of the V. cholerae genome, suggesting the potentia of these strains for accepting the horizontal transfer of virulence factor genes. Thus, continuous survey of the vibrio is to ensure the food safety of fishery products.