Studies were performed to evaluate the suitability of cyclone scrubber samplers and a continuously wetted substrate for detection of several types of microorganisms. The samplers were evaluated in a dynamic aerosol chamber using all-glass impingers as reference samplers. Comparison of a stainless steel and a glass cyclone scrubber sampler for detecting Bacillus subtilis var. niger spore aerosols of about 1.1-3.3 micrometers count median diameter showed no significant differences in their relative collection efficiencies. Based upon ease of construction, present usage, and potential availability, the glass cyclone scrubber was selected for further evaluation. This sampler showed geometric mean relative collection efficiencies, for B. subtilis var. niger spore aerosols, of 52% and 68%, depending upon the composition of the disseminating fluid. In studies using different organisms, in similar sized aerosols, this relative efficiency was 46% for Serratia marcescens, 76% for f(2) coliphage, and 92% for poliovirus type 1. During the process of aerosolization and collection, the greatest viability losses in both the reference and cyclone scrubber samplers were observed with poliovirus, followed by f(2) coliphage, and S. marcescens. It was recommended that methods used for detection of ambient viable microbial aerosols be standardized, that a selected standard sampler be evaluated under a wide range of conditions for optimization of critical parameters, and that relative microbial aerosol evaluations be performed with a reference sampler having a sensitivity similar to that of the test sampler.