The report, a user guide, describes the capabilities and use of the Particulate Data Reduction (PADRE) system, an interactive computer program that facilitates entry, reduction, and analysis of cascade impactor data for particle size distributions. Example sessions are provided to illustrate the system's capabilities. Calculations, algorithms, and messages are documented in a separate PADRE reference manual. PADRE was developed to ensure the quality of data included in the Fine Particle Emissions Information System (FPEIS), which is the particle size measurements component of the Environmental Assessment Data Systems (EADS). Users control the logical flow through the system in response to prompts from the program. PADRE can be used to store, review, edit, and analyze data and, through a variety of data checks, to identify invalid or suspect data. Impactor stage cut points can be calculated; cumulative and differential mass concentrations can be determined and interpolated to standard diameters. The PADRE system, installed at EPA's National Computation Center at Research Triangle Park, may be made available to users of cascade impactors.