A clear understanding of microbial sampler's ability to recover culturable bioaerosols is essential for better exposure estimate and design of future advanced samplers. This research investigated the physical and biological parameters affecting overall performance of portable microbial samplers when collecting different bioaerosol species. Seven portable samplers with impaction velocity from 1 to 15 m/s and jet-to-plate distance from 1.7 to 6 mm were used. Three bacterial and fungal species were aerosolized and collected by the samplers under controlled humidity, 40-45%. The ability of portable impactors to recover culturable bioaerosols was compared to that of an Andersen-type impactor and a Button Aerosol Sampler equipped with gelatin filter and their relative overall performance was determined. Experimental data indicated that performance of portable microbial samplers varied from model to model, and depended on investigated bioaerosol species. When sampling bacterial species, the relative overall performance of the impactors was highly correlated with their collection efficiency (adjusted R-2 = 0.74-0.94) and inclusion of samplers' jet velocity and jet-to-plate distance into multiple liner regression did not affect the adjusted R-2 values. In contrast, when sampling fungi, use of the collection efficiency in the linear regression as the sole predictor of the impactors' relative overall performance yielded adjusted R-2 values ranging from 0.61 to 0.73; inclusion of jet velocity and jet-to-plate distance into multiple liner regression increased the adjusted R-2 values to the range of 0.75-0.89. ne data demonstrate that in addition to collection efficiency, jet velocity and jet-to-plate distance also play an important role in the enumeration of bioaerosols by microbial impactors. The results from this investigation could be helpful in selecting and designing microbial samplers for assessing bioaerosol load in various environments. (C) 2006 Elsevier Ltd. All rights reserved.