A bacteriophage-typing scheme for Vibrio cholerae has been developed on the basis of the pattern of susceptibility of V. cholerae strains to four groups of freshly isolated cholera bacteriophages. Some 4066 strains of V. cholerae isolated in Calcutta during the period 1955-61 have been classified into seven types and subtypes. Less than 1% of the strains were untypable. No correlation was found to exist between the phage-types and serological types of V. cholerae. In lysogenic strains, however, a correlation was observed between the phage-types of V. cholerae and their lysogenic phages. Groups of infection deriving from a single source were found to be caused by single phage-types. The author also discusses the practical value of the phage-typing scheme for the epidemiological investigation of cholera.