Several researchers have documented variability among soil testing labs in analytical results returned for the same sample. Reasons for this variability include the use of different extract and analytical methodologies, as well as errors. In many states, USDA-NRCS Code 590 standards now restrict nutrient applications based on soil test results. This increased reliance on soil test results for nutrient management planning has placed greater emphasis on lab proficiency. The North American Proficiency Testing (NAPT) program was developed to provide a mechanism for labs to voluntarily and confidentially identify and correct analytical problems. Among Western U.S. states, most Code 590 standards now require producers to send soil samples to a lab enrolled in the NAPT program in order to receive funding from USDA farm programs (EQIP, CSP, etc.). In 2002, livestock producers in Utah discovered that they could obtain soil test phosphorus values below Code 590 thresholds for manure application by sending samples to certain labs that were enrolled in the NAPT program but not performing well. Poor performance of certain NAPT program labs was documented in blind sample comparisons conducted in Utah, and later in Washington State. Little could be done to influence the performance of labs in the NAPT program. In 2003, representatives from Western U.S. land grant universities, the USDA-NRCS, and the soil testing lab industry met with directors of the NAPT program in Salt Lake City to discuss options for a more stringent proficiency program. The decision was made to develop the pilot Performance Assessment Program (PAP) as an addition to the NAPT program. The PAP required labs to demonstrate a certain level of performance relative to their peers based on blind samples. Labs that do not meet performance standards are not permitted to analyze samples for producers receiving USDA farm program funds.