STRAINS of Alcaligenes faecalis (unpublished observations) previously used1 are not inhibited by colicines A–K and V apart from A. faecalis strain N.C.T.C. 8769, which is inhibited by colicinogenic strains CA 38, CA 23, CA 42, CA 46, CA 57, CA 58, CA 62 and P 14, kindly supplied by Prof. P. Fredericq.