Abstract: The metabolism of boldenone (17β-hydroxy-1,4-androstem-3 -one) in man has been investigated by gas chromatography/mass spectrometry. After oral administration of a 20 mg dose to man, six metabolites were detected in the conjugated fraction of the urinary samples. Boldenone, the major compound excreted in urine, was detected within 34 h after administration.In addition , several metabolites, resulting from the hydroxylation of boldenone and the reduction of the unsaturated carbon bonds of boldenone,were detected in the urine samples varying from 9 to 83 h. Extraction and fractionation of these metabolites were achieved by using XAD- 2 column and gas chromatography. The recovery of the whole procedure was studied. Furthermore, the mass spectra of the metabolites are presented and major fragment pathways are discussed.