The metabolism and excretion of androst-4-ene-3,6,17-trione after administration of the ‘nutritional’ supplement 6-OXO® was investigated by gas chromatography–mass spectrometry (GC-MS) in full-scan mode. The parent drug androst-4-ene-3,6,17-trione and androst-4-ene-6α,17β-diol-3-one and androst-4-ene-6α-ol-3,17-dione were detected in the post-administration urine samples. Because androst-4-ene-3,6,17-trione is an anabolic steroid and an aromatase inhibitor, this substance is regarded as a doping agent. Hence, a selective and sensitive GC-MS method in selected ion monitoring mode for the detection of the TMS-enol-TMS-ether derivatives of these substances was developed and validated for doping control purposes. The limit of detection (LOD) of the investigated compounds ranged from 5 to 10 ng[sol ]mL. Using this method, the detection time for androst-4-ene-3,6,17-trione and androst-4-ene-6α,17β-diol-3-one was 24 h, while androst-4-ene-6α-ol-3,17-dione could be detected up to 37 h after administration of the dose recommended by the manufacturer. Copyright © 2005 John Wiley & Sons, Ltd.