Abstract A sensitive method for the simultaneous determination of quazepam and two of its metabolites, 2-oxoquazepam and 3-hydroxy-2-oxoquazepam, in human urine was developed using gas chromatography–mass spectrometry (GC/MS) with an Rtx-5MS capillary column. The quazepam and its metabolites were extracted from human urine using a simple solid-phase extraction Oasis® HLB cartridge column, and the 3-hydroxy-2-oxoquazepam was derivatised using BSTFA/1%TMCS and pyridine at 60°C for 30min. The mass spectrometric detection of the analytes was performed in the full scan mode, m/z 60–480, and selected ion monitoring (SIM) mode, m/z 386, for quazepam; m/z 342, for 2-oxoquazepam; m/z 429, for 3-hydroxy-2-oxoquazepam-TMS; and m/z 284, for alprazolam-d5 (internal standard), by electron ionization. The calibration curves of quazepam and its metabolites in urine showed good linearity in the concentration range of 2.5–500ng/0.2ml of urine. The average recoveries of quazepam and its metabolites from 0.2ml of urine containing 500ng and 50ng of each drug were 71–83% and 88–90%, respectively. The limits of detection of quazepam, 2-oxoquazepam and 3-hydroxy-2-quazepam in urine by the selected ion monitoring mode were 0.096–0.37ng/ml. This method would be applicable to other forensic biological materials containing low concentrations of quazepam and its metabolites.