Fourteen restriction endonucleases (ENases) were found by screening of 118 O antigen reference strains of Vibrio cholerae. Ten of these ENases were partially purified and classified into eight specificity categories. All of them were isoschizomers of already-known ENases. It is of interest that the isoschizomer of EcoRI ENase designated VchO2I was found in V. cholerae O2, since VchO2I, as well as EcoRI, shows high activity at pH 8 approximately 9, and most V. cholerae strains can grow well in this pH range.