Abstract: A process for the isolation of nontoxinogenic V. cholerae strain and a process for preparing a cholera vaccine from said V. cholerae strain, said process comprising (a) isolating V. cholerae from the stool of a patient suffering from cholera by spreading the stool on a selector medium specific for V. cholerae, (b) separating the non-toxinogenic V. cholerae strain from the population of the V. cholerae strains isolated in step (a), and (c) incorporating immunogenic cholera toxin (ctx) B subunit gene into the chromosome of the strain by conventional methods to produce the vaccine.