19-Nor-4-androstenediol is a prohormone of nandrolone. Both substances are included in the WADA list of prohibited classes of substances. The aim of this study is to determine the plasma levels of 19-nor-4-androstenediol and its metabolites after oral administration of a nutritional supplement containing the drug. Two capsules of Norandrodiol Select 300 were orally administered to six healthy male volunteers. Plasma samples were collected up to 24 h. Samples were extracted to obtain free and glucuronoconjugated metabolic fractions. Trimethylsilyl derivatives of both fractions were analyzed by gas chromatography coupled to mass spectrometry (GC-MS). The method was validated to determine linearity, extraction recovery, limit of detection and quantification, intra- and inter-day precision and accuracy. After administration of 19-nor-4-androstenediol, the main metabolites detected were norandrosterone and noretiocholanolone, mainly in the glucuronide fraction. Nandrolone, norandrostenedione and 19-nor-4-androstenediol were also detected at lower concentrations. © 2008 Elsevier Inc. All rights reserved.