The physical sampling efficiency of three commonly used samplers for bioaerosols has been determined under controlled conditions in a wind tunnel. Non-biological, monodisperse test aerosols of aerodynamic diameters up to 23 mum were used in a range of wind speeds up to 5 m s-1. The performance of each sampler type was different. For the Andersen Microbial Sampler and the Casella Slit Sampler, sampling efficiency dropped both with increasing wind speed and particle size, while for the Aerojet General Glass Cyclone, performance was generally independent of windspeed and particle size. This work is part of a larger study to determine both the physical and the biological sampling efficiencies of currently used samplers for bioaerosols. The results highlight the importance of understanding the performance of aerosol monitoring equipment, if results obtained in the field are to be interpreted correctly.