Effective regulation, enforcement, and litigative action by the United States Environmental Protection Agency's Office of Pesticides and Toxic Substances are predicated upon the evaluation of scientifically valid and environmentally meaningful data on a chemical's potential impact on the environment. Industry must provide EPA with the results of tests designed to forecast potential ecological effects and the probable environmental fate of a candidate chemical substance and/or mixture (i.e., test substance). To this end, EPA has guidelines to allow effective comparison of results used in the assessment process. For the data to be comparable however, the test must be performed in the same rigorous manner with only slight, yet documented variation allowed. Thus, protocols or standard procedures for performing the tests must be documented for industry to ensure development of comparable data bases. This protocol is one which could be added to a series of tests recently developed as guidelines for Section 4 of the Toxic Substances Control Act. The terrestrial soil-core microcosm is designed to supply site-specific and possibly regional information on the probable chemical fate and ecological effects resulting from release of a chemical substance to a terrestrial ecosystem. The EPA will use the data resulting from this test system to compare the potential hazards of a chemical with others that have been previously evaluated.