A rapid immunoassay for the detection of specific PCR products is described in which a positive PCR amplification result is detected, usually in less than 5 min, by applying a few drops of the diluted PCR end-product to a small immunoassay sample device. The method was evaluated in comparison with conventional susceptibility tests and isoelectric focusing (IEF) for the detection of TEM-family beta-lactamase genes in 477 Escherichia coli isolates from urine samples. Of 187 isolates identified as presumptive TEM beta-lactamase producers by conventional methods, 185 generated a positive signal in the PCR immunoassay system. Two further signal-positive isolates were recognised when the PCR was repeated. In addition, one of the 276 ampicillin-susceptible isolates gave a positive signal in repeated PCR-immunoassay experiments despite being ampicillin susceptible and failing to give a TEM-type enzyme band in iso-electric focusing experiments.