- An enantioselective HPLC method for the simultaneous determination of the concentration of the enantiomers of the oxcarbazepine metabolites 10-hydroxycarbazepine (MHD) and carbamazepine-10,11- trans -dihydrodiol (DHD) in human urine is described. The method is based on extraction with tert .-butylmethyl ether–dichloromethane (2:1, v/v) under alkaline conditions, separation and evaporation of the organic phase and dissolution of the residue in the mobile phase. Enantiomers are resolved on a Diacel Chiralcel OD column (250 mm×4.6 mm I.D.) under isocratic conditions using as mobile phase n -hexane–ethanol–2-propanol (18:2:1, v/v/v) with addition of glacial acetic acid (0.1%). The enantiomers are detected by UV at 215 nm. The method allows reliable determination of the MHD and DHD enantiomers in human urine with limits of quantification of 0.2 mg/l and 0.4 mg/l, respectively.