In Dacca, Bangladesh, potent enterotoxin-producing Escherichia coli were isolated from many hospital cases of acute cholera-like diarrhea. Enterotoxigenic (tox+) and non-enterotoxigenic (tox−) isolates of E. coli were used to investigate possible means of differentiating tox+E. coli from those (tox−) of the normal flora. The majority (81%) of the tox+E. coli studied were found to be negative for sucrose fermentation, 85% exhibited retarded growth in a peptone medium at pH 8.5, and 92% released large amounts of ammonium sulfate precipitable materials into culture supernatant fluids; 66.6% exhibited all three of these properties. For the tox− group the respective values were found to be 50%, 31%, and 34%; only 9.3% exhibited all three properties. These results indicate that it may be possible to use phenotypic characteristics other than antigenic composition and enterotoxin production for the identification of enterotoxigenic E. coli.