The comparative study of the genomes of V. cholerae O139 isolated from humans and from water of surface reservoirs was carried out with the use of single- and double-primer polymerase chain reaction (PCR). The profiles of polymorphic DNA fragments obtained in this study made it possible to find out differences between groups of strains, as well as the individual features of some of them. The comparison of strains isolated from humans and from water in single-primer PCR revealed that they, in spite of the general similarity of their genomes, essentially differed, which was probably due to changes in the genome of this infective agent. Strains of aqueous origin lacked genes ctx and tcpA, which made them epidemiologically unimportant.