The efficacy of using sampling heads with smaller holes to collect small particles as part of a larger study evaluating bioaerosols in indoor environments was studied. In an attempt to increase the particle collection efficiency, the manufacturer had machined three different sampling heads, each with smaller holes than the standard sampling head. A fourth sampling head was also used which was available commercially and had more of the same size holes than the standard sampling head. An Andersen six stage sampler was used simultaneously with two surface air system (SAS) samplers to sample indoor air in two office environments. There were no significant differences in the results regarding the concentration of bacteria and fungi collected among the four sampling heads regardless of which sampler model was used in a small sample at either of the two office sites. Results changed, however, with the addition of 15 samples at one site, where three of the four sampling heads statistically undersampled the six stage sampler and the other sampling head. The author suggests that the Pitot Validation Kit (PVK) may be used as an accurate flow rate measurement device with the SAS-HF sampler, though the Pitot tube measures only centerline velocity pressure. The author concludes that due to the 10% decrease in flow rate which comes about from the pressure drop across the PVK, a reasonable estimate of flow rate through the SCS-C sampler is provided by the equation in the manufacturer's literature for calculating average velocities.