E. coli XL1-B cells, genetically modified to contain the gene for the commerically important food-processing enzyme, bovine chymosin, were aerosolised in growth media to simulate a breach of containment. Aerosols were generated in a well-characterised bioaerosol test chamber, and sampled using two commonly employed workplace aerosol samplers-the Cyclone static ＇＇area＇＇ sampler, and the IOM Personal Inspirable Aerosol Sampler. PCR-based detection procedures were developed for the specific, sensitive, and rapid, detection and discrimination of both captured aerosolised genetically modified and unmodified E. coli cells. The IOM personal sampler proved to be more useful than the cyclone sampler for aerosol capture and subsequent analysis using the PCR procedure. It allowed an apparent lower limit of detection of an aerosol containing 1.7 x 10(4) cells m(-3), with results being obtained within 4-5 h after sample collection.