The following eight bioaerosol samplers were evaluated: an Andersen six stage microbial particle sizing sampler (6STG), an Andersen two stage microbial particle sizing sampler (2STG), an Andersen single stage microbial particle sampler (1STG), a Pool Bioanalysis Italiana surface air system sampler (PBI), a Mattson-Garvin slit to agar air sampler (STA), a Biotest Reuter centrifugal air sampler (RCS), a Gelman 47 millimeter membrane filter air sampler (MF), and an Ace Glass all glass impinger-30 sampler (AGI30). The aerosols were of single cells of Escherichia-coli and Bacillus-subtilis bacteria at concentrations of approximately 2000 and 1200 colony forming units per cubic meter (m3), respectively. The air flow rate inside the chamber was 11.3m3 per minute. A second AGI30 sampler located approximately 0.6 meter upstream from the tested samplers served as the reference. The collection efficiencies of the 6STG, 2STG, 1STH, PBI, STA, RCS, MF, and AGI30 samplers were determined. The mean efficiencies for collecting E-coli of the samplers relative to the reference AGI30 sampler were: 6STG 1.071, AGI30 1.001, 1STG 0.934, STA 0.887, 2STG 0.681, PBI 0.00089, RCS 0.00028, and MF below subtilis were: 6STG 1.059, AGI30 1.014, 1STG 0.926, STA 0.907, 2STG collection efficiency of the MF sampler for E-coli was attributed to the bacteria becoming desiccated on the membrane filter. The authors conclude that the tested samplers show a wide variability in their ability to sample free bacteria. The high relative collection efficiencies of the 6STG, 1STG, and AGI30 make them the samplers of choice.