The U.S. Environmental Protection Agency (EPA) in conjunction with the U.S. Department of Agriculture is currently testing a protocol for determining the 'Aerobic Degradation Potential of Hazardous Organic Constituents in Soil' to ensure its reliability, accuracy, cost effectiveness, and ease of use. This protocol is part of EPA's Office of Research and Development efforts to provide Federal and State EPA offices as well as consultants and industries with guidelines and encouragement for conducting standardized treatability studies. Testing of the protocol has been initiated with standardized soil (obtained from EPA's Synthetic Soil Matrix, Edison, NJ). Two surrogate pollutants, toluene, a volatile, and phenol, a semivolatile, are being tested as representative, easily biodegradable compounds. Critical aspects of the protocol involving the configuration of the test reactor and procedures for trapping the volatiles have been identified. Once fine tuning of the process is completed, testing of combinations of compounds in a variety of soil matrices is planned.