Summary:The methods suggested in the Report of the Coliform Sub‐Committee of the Society for Applied Bacteriology (Report, 1949) have been used in isolating and studying the coli‐aerogenes content of 142 samples of farm water supplies in two distinctive areas of Britain. The Gram‐negative cultures were grouped into typical, anaerogenic, non‐lactose‐fermenting and ‘unclassifiable’types, forming 54.2, 2.9, 10.9 and 32.0% of the 384 cultures respectively. Among the 261 coli‐aerogenes cultures,Bact. coli, intermediate and aerogenes‐cloacae organisms were found with frequencies of 32.2, 19.5 and 48.3% respectively. The majority of anaerogenic coli‐aerogenes organisms resembledBact. colitype II while the predominant non‐lactose‐fermenters resembledBact. cloacaeandBact. aerogenestype I. The reactions of 123 ‘unclassifiable'strains were such that very few could be regarded asBact. colitypes owing to the high incidence of gelatin liquefaction an