The Environmental Protection Agency (EPA) and its predecessor organizations historically have devoted considerable time and effort to the standardization of test procedures, the development and use of calibration and performance audit procedures, quality control and reference samples, training, and other quality assurance (QA) activities. However, these QA activities were essentially voluntary, and most of the data generated were reported with no indication of quality, thereby severely reducing their usefulness. Due to questions concerning the quality of EPA's data, Agency policy stipulated on 30 May and 29 June 1979 requires participation in a centrally managed QA program by all organizational units engaged in environmentally related measurements. This policy applies equally to those extramural efforts performed on behalf of EPA. The primary responsibility for program development and direction is assigned to the Office of Research and Development, while other program offices, regions, and laboratories are responsible for its implementation. Essential elements of the program include developing and implementing QA program plans, QA project plans, and standard operating procedures; conducting audits of the capability and performance of measurement systems, and data quality; maintaining a mechanism for corrective actions; QA training; and frequent reports to management on the quality of data, program effectiveness, and problems. The goal of the QA program is to ensure that all data generated are of known, documented, and acceptable quality.