Enterotoxigenic Escherichia coli was studied in waste water, river water, and seawater from six locations along the west coast of Normandy by using the polymerase chain reaction (PCR) to amplify the heat labile (LT) gene. Cellular DNA was extracted from centrifugation pellets and amplified using PCR. The PCR products were detected by gel electrophoresis and confirmed by hybridization assay, using an 850 base pair HindIII DNA fragment probe from pEWD299 conjugated to digoxigenin and specific for the LT gene. Results of the PCR amplification were compared with those of GM1 enzyme-linked immunosorbent assay, latex agglutination, and colony hybridization. The PCR method was found to be more precise and less time consuming, especially when compared with methods requiring culture of isolates for enumeration of enterotoxigenic E. coli in water.