The paper discusses quality control (QC) for stationary source particle size measurements. Traditional QC methodology has generally involved retrospective evaluation of existing products (e.g., environmental data). Rather than identify failures, it is now increasingly possible and desirable to provide increased QC support to the production of data; i.e., doing it right the first time. It is clear from many disciplines that timely feedback mechanisms are one of the easiest, least expensive means of providing the support. In addition to some of the considerations related to source emissions testing, these concepts have been applied to cascade impactor testing. The Particle Data Reduction (PADRE) system offers a standard, quality assured data reduction method and protocol for particle size testing of stationary point sources using cascade impactors. The utilization of PADRE in testing has, to date, produced improved quality assurance documentation and greater confidence in the quality and credibility of the measurements data obtained.