Organic audit materials have been developed by U.S. Environmental Protection Agency to evaluate quality of measurements made by federal, state, and local agencies or their contractors during compliance source tests. Among audit materials are materials for auditing EPA Method 25, a method for measuring source emissions of volatile organic compounds. Two types of audit materials for Method 25 have been developed and validated by inter- and intra-laboratory studies. The first type makes use of commercially available gas cylinders containing known concentrations of selected volatile organics in an inert balance gas. The second type involves use of a stainless steel cartridge containing a solid sorbent (Tenax) spiked with known quantities of selected organic compounds to generate organic vapors quantitatively using thermal desorption. Results indicate both types of audit materials are stable and useful in conducting EPA Method 25 audits.