There is concern currently over the accuracy of the Federal Reference Method (FRM) PM2.5 sampler, which is used to measure ambient concentrations of particulate matter (PM) less than 2.5 micrometers. The primary concern is that EPA is mandating that the FRM PM2.5 sampler be used to measure ambient concentrations of PM2.5 and that the sampler is a PM2.5 sampler based on "design" rather than by "performance". Very little performance data has been published or released by EPA. This FRM sampler was designed using the same engineering principles as the cascade impactor, which presently, is the EPA approved method for determining particle sizing characteristics such as a particle size distribution (PSD) i.e. a distribution of particle mass versus its aerodynamic equivalent diameter (AED). The only other accessible method to obtain a PSD of PM mass versus AED is by using the Coulter Counter Multisizer (CC). The purpose of this paper is to report preliminary results of PSDs utilizing the cascade impactor and CC. In addition, inferences were made from the results as to anticipated problems relative to the performance of the FRM PM2.5 sampler and its potential inaccuracies.