In recent years products containing 6α-methylandrost-4-ene-3,17-dione have appeared on the sport supplement market. Scientific studies have proven aromatase inhibition and anabolic and mild androgenic properties; however, no preparation has been approved for medical use up to now. In sports 6α-methylandrost-4-ene-3,17-dione has to be classified as a prohibited substance according to the regulations of the World Anti-Doping Agency (WADA). For the detection of its misuse the metabolism was studied following the administration of two preparations obtained from the Internet (Formadrol and Methyl-1-Pro). Several metabolites as well as the parent compounds were synthesized and the structures of 3α-hydroxy-6α-methyl-5β-androstan-17-one, 6α-methylandrost-4-ene-3,17-dione, and 5β-dihydromedroxyprogesterone were confirmed by nuclear magnetic resonance (NMR) spectroscopy. The main metabolite, 3α-hydroxy-6α-methyl-5β-androstan-17-one, was found to be excreted as glucuronide and was still detectable in µg/mL amounts until urine collection was terminated (after 25 h). Additionally, samples from routine human sports doping control had already tested positive for the presence of metabolites of 6α-methylandrost-4-ene-3,17-dione. Screening analysis can be easily performed by the existing screening procedure for anabolic steroids using 3α-hydroxy-6α-methyl-5β-androstan-17-one as target substance (limit of detection <10 ng/mL). Its discrimination from the closely eluting drostanolone metabolite, 3α-hydroxy-2α-methyl-5α-androstan-17-one, is possible as the mono-TMS derivative. Copyright © 2008 John Wiley & Sons, Ltd.