COLICINES originally demonstrated in E. coli have since been found in many other Gram-negative bacilli present in the intestine, Ps. pyocyanea and some Gram-positive bacilli1–4. Such antibacterial substances are now called bacteriocines5. It has also been confirmed that bacteria of different genera may produce a similar colicine6 and that the range of antibacterial activity of colicines exhibits interesting specificities3,4. The possible role of bacteriophages, colicines and other factors producing disintegration of vibrios with subsequent liberation of toxin has been postulated to explain the pathogenesis of cholera7 which prompted this investigation into the colicinogenicity and colicine-susceptibility of 60 strains of V. cholerae (45 Inaba and 15 Ogawa) and 15 strains of El Tor vibrios. Sixteen standard colicinogenic strains producing different types of colicines and 4 colicine-sensitive indicator strains were kindly presented by Prof. P. Fredericq of the University of Liege.