A novel gas chromatography-mass spectrometric (GC-MS) method was developed to confirm and identify metoprolol and its metabolites by double derivatization with S-(-)menthyl chloroformate [(-)-MCF] and N-methyl-(trimethylsilyl)-trifluoroacetamide (MSTFA). This is the first report, which describes the simultaneous identification of metoprolol, its one major acidic and other basic metabolites in human urine based on solid-phase extraction with C18reversed-phase cartridges.