The benefits of particle counting and size distribution analysis as aids in evaluating water treatment processes and for determining process efficiency have been recognized for over a decade. Currently, particle counting is being considered as the measurement technique to determine cyst removal credit as specified in the Surface Water Treatment Rule. If sufficient particle reduction can be demonstrated--say 2 log (99 percent removal)-disinfection levels may be reduced accordingly. By this means, health risk from disinfection byproducts (DBPs) would be reduced without unduly increasing health risk from pathogens. The following presents data that reaffirm the value of particle counting for process evaluation but points out the shortcomings of a "one size fits all" approach in using particle removal efficiencies for regulatory purposes.