The urinary metabolism of the irreversible aromatase inhibitor androsta-1,4,6-triene-3,17-dione was investigated. It is mainly excreted unchanged and as its 17beta-hydroxy analogue. For confirmation, 17beta-hydroxyandrosta-1,4,6-trien-3-one was synthesized and characterized by nuclear magnetic resonance (NMR) in addition to the parent compound. In addition, several reduced metabolites were detected in the post-administration urines, namely 17beta-hydroxyandrosta-1,4-dien-3-one (boldenone), 17beta-hydroxy-5beta-androst-1-en-3-one (boldenone metabolite), 17beta-hydroxyandrosta-4,6-dien-3-one, and androsta-4,6-diene-3,17-dione. The identification was performed by comparison of the metabolites with reference material utilizing gas chromatography/mass spectrometry (GC/MS) of the underivatized compounds and GC/MS and GC/tandem mass spectrometry (MS/MS) of their trimethylsilyl (TMS) derivatives. Alterations in the steroid profile were also observed, most obviously in the androsterone/testosterone ratio. Even if not explicitly listed, androsta-1,4,6-triene-3,17-dione is classified as a prohibited substance in sports by the World Anti-Doping Agency (WADA) due to its aromatase-inhibiting properties. In 2006 three samples from human routine sports doping control tested positive for metabolites of androsta-1,4,6-triene-3,17-dione. The samples were initially found suspicious for the boldenone metabolite 17beta-hydroxy-5beta-androst-1-en-3-one. Since metabolites of androst-4-ene-3,6,17-trione were also present in the urine samples, it is presumed that these findings were due to the administration of a product like 'Novedex Xtreme', which could be easily obtained from the sport supplement market.