The U.S. Environmental Protection Agency's Indoor Environment Management Branch (IEMB) has designed and installed a state-of-the-art large indoor air quality test chamber in their Research Triangle Park facility. The room-sized (30 cu m) stainless steel test chamber and sophisticated analytical instrumentation will permit characterization of emissions from products and processes that cannot readily be studied using small chambers. Tests have been conducted that were designed to evaluate critical factors that may influence experiments. These tests evaluated (1) chamber system air leakage rate; (2) the ability of the chamber control system to maintain a wide variety of temperature and relative humidity set points; (3) air speed within the chamber at different flow conditions; and (4) mixing of pollutants at different flow and temperature conditions. Results of these tests how the capabilities of the large chamber system, demonstrate its limitations, and point to opportunities for improving its operation.