ABSTRACT Local, state, regional, and national precipitation chemistry networks have been established during the last twenty-five years in an effort to assess temporal and spatial patterns in atmospheric deposition. * These networks have been implemented with varied objectives but they all involve the collection and chemical analysis of precipitation. Interpretation of the data generated from these various measurement programs has been complicated by the different sampling and analytical protocols that have been employed. This is particularly true of historical data sets that do not include complete information on the analytical methodologies used, bias and precision of reported chemical results, or quality assurance practices. These procedural differences, combined with a lack of adequate documentation, have resulted in nonuniform data sets that make trend analysis difficult. To provide the scientific community with a set of standardized procedures for the collection and analysis of precipitation samples, the Illinois State Water Survey has developed an analytical methods manual for use in acid deposition studies. This manual includes detailed methods documentation for the major inorganic constituents of interest in wet deposition as well as guidelines for the collection, preservation, and processing of samples. The importance of a comprehensive quality assurance program is emphasized for all aspects of a precipitation chemistry measurement system. The analytical methodologies include flame atomic absorption spectrophotometry, ion selective electrode, automated colorimetry, ion chromatography, and titrimetric procedures. These methods were selected for inclusion based on their sensitivities, accuracy, and freedom from significant chemical and physical interferences. The instrumentation required for these methods is available in most laboratories involved with water analyses so that the procedures described will be useful to as many researchers as possible. The adoption of standard test procedures will lead to greater comparability between laboratories reporting precipitation chemistry data and will improve the reliability of data interpretation efforts.