The detection of cholera enterotoxin in environmental objects and isolation of patients are considered to be the most reliable indices of that the cholera agent is present. Described in the case study is a method of nested polymerase chain reaction (PCR) based on amplifying the ctxA gene fragment coding subunit A of enterotoxin. A possibility was shown to use the above method to confirm the virulence of strains Vibrio cholerae isolated from different sources. The method was tested with 18 virulent and avirulent strains V. cholerae as well as (for the sake of verifying the analysis specificity) with DNAs of other human-pathogenic microorganisms and with the human genome DNA. The results showed a high efficiency of nested PCR in detecting the pathogenicity of cholera-agent strains.