The Drug Enforcement Administration (DEA) reports that as of October 2010, 79% of all cocaine seized in the United States contained levamisole. The equine conversion of levamisole to aminorex has been demonstrated. However, the metabolic fate of levamisole in humans is unknown. Nevertheless, as aminorex is amphetamine-like and hallucinogenic, it may be used as an adulterant to increase the effects of cocaine. We report here the results of in vivo studies demonstrating for the first time that not only equine, but also canine and human metabolism all result in aminorex formation. Levamisole and aminorex were extracted from real urine samples by liquid-liquid extraction and identified and quantified by GC-MS (identification by 3 ions per substance, LLOQ at 0.15 ng/ml for both). (C) 2011 Elsevier B.V. All rights reserved.