A repository has been established by EPA to provide audit materials to federal, state and local agencies or their contractors for use in performance audits to assess the accuracy of measurement methods used during (1) hazardous waste trial burns, (2) compliance source testing, and (3) ambient air measurements. This repository currently contains 21 gaseous organic compounds in five-, seven-, and nine-component mixtures at parts-per-billion (7 to 10,000 ppb) levels and 40 gaseous organic compounds at parts-per-million (5 to 700 ppm) levels in compressed gas cylinders. Performance audits have been conducted using the repository gases to assess the accuracy of the measurement methods. Seventy-six and one hundred sixty-one performance audits to date have been initiated using ppb and ppm level audit gases, respectively. The audit results obtained with the ppb level component mixtures during hazardous waste trial burn tests were generally within + or - 50% of the EPA concentrations. The audit results obtained with the ppm level organics during compliance source tests were generally within + or - 15% of the EPA concentrations. The list of organics in the audit repository, stability data, and results of representative performance audits are described.