Enantiomeric compositions of methamphetamine (MA) and its major metabolite, amphetamine (AP), in the urine of mice administered with l-deprenyl (DPN), d-methamphetamine and dl-methamphetamine were analysed by the selected ion monitoring of gas chromatographmass spectrometry (GC-MS) using a chiral reagent. Each drug was intraperitoneally administered to mouse at 0.1, 0.5, 1mg/kg and urine samples of each two mice in a cage were collected at 0-12, 12-24, 24-48 and 48-72h, respectively. Urine added with deuterium-labelled MA and AP as the internal standards were applied to Bond Elut C18 and eluted with acidic methanol. The extract was evaporated to dryness and the residue dissolved in 0.1ml of chloroform containing 10% triethylamine and added with 0.05ml of 0.1M N-trifluoroacetyl-l-proryl chloride in chloroform. The derivatives were analysed by GC-MS on an OV-1 bonded capillary column (10m×0.25mm). The apparent d/l of MA excreted in the urine of mice by the administration of l-DPN, d-MA and dl-MA were 0-0.06, 3.20-6.76 and 1.04-1.71, respectively. The ratio of AP/MA in the urine by the administration of l-DPN, d-MA and dl-MA were approximately 1 : 2, 1 : 20 and 1 : 20, respectively. By use of these two factors it is possible to discriminate l-DPN use from MA use.