The polymerase chain reaction (PCR) and biological methods for detection of enterotoxigenic strains of Escherichia coli were compared. The tests for LT, STa and STb were done in the cell line Y1, suckling mice, and ligated piglet intestinal loops, respectively. The production of STb was tested only in strains negative for LT and STa. The polymerase chain reaction has proved to be specific and reliable method than the biological methods. Unlike the latter, PCR allows the detection of strains producing in vitro only low quantities of the toxin. On the other hand, PCR fails to identify strains producing toxic substances with a different structure but the same or similar biological properties.