The analytical and methodological imperatives for large-scale and routine gas chromatographic-mass spectrometric screening of anabolic steroid urinary metabolites are described. Several aspects of their isolation, enzymatic hydrolysis, derivatization and metabolism in humans are discussed. Gas chromatographic-mass spectrometric data illustrating artifacts arising from enzymatic hydrolysis of 3 beta-ol-5-en steroids, and describing new metabolites of boldenone, methanedienone and stanozolol, as well as the conversion of norethisterone into 19-nortestosterone metabolites through de-ethylation at C-17, are presented. The analytical approach developed for gas chromatographic-mass spectrometric screening of anabolic steroids is based on the sequential selection-ion monitoring of specific and discrete ion groups characteristic to the steroids of interest under high-resolution chromatographic conditions. The major analytical and methodological requirements necessary to provide irrefutable evidence, in the case where the presence of a synthetic anabolic steroid or a testosterone to epitestosterone ratio higher than 6:1 is suspected in a given urine specimen, are also discussed.