Two studies were conducted to compare the results of the Toxicity Characteristic Leaching Procedure (TCLP) with those of the Extraction Procedure Toxicity Characteristic (EP). In the first study, a synthetic heavy metal waste was chemically solidified/stabilized with and without a variety of interfering compounds. The solidified/stabilized waste was cured for 28 days and subjected to the TCLP and EP extractions. The extracts were analyzed for Cd, Cr, Ni, and Hg. In the second study, two solidified/stabilized, heavy metal wastes and an untreated perchloroethene (PCE) still-bottom waste were used. Twelve volatile organic compounds were added to each waste type at two ratios. The EP and TCLP were performed on three samples from each waste type. The extract from each sample was analyzed for As, Ag, Ba, Cd, Cu, Ni, Pb, and Zn and the 12 volatile organic compounds. The losses due to the mechanics of the TCLP and EP extracts with know concentrations of organic compounds before and after extracting the wastes. Results of these studies indicate that, for most of the metal contaminants, the TCLP and EP produce similar results when TCLP extraction fluid 2 (acetic acid solution) is used but differ when TCLP extraction fluid 1 (acetate buffer) is used. The results of testing for volatile organic contaminants indicate that, for 8 of the 12 contaminants, the concentrations measured in the TCLP leachates were significantly greater that those measured in the EP leachates.