A high-performance liquid chromatography (HPLC) assay was developed for the determination of alprazolam and its active metabolite, α-hydroxyalprazolam, in human plasma. Alprazolam, α-hydroxyalprazolam and estazolam as an internal standard were detected by ultraviolet absorbance at 230nm. Alprazolam and α-hydroxyalprazolam in plasma were extracted by a rapid and simple procedure based on cyanopropyl bonded-phase extraction. A C₈ reversed-phase HPLC separation technique was developed. Determination of alprazolam was possible in the concentration range at 1.0-50ng/ml and α-hydroxyalprazolam in range at 0.5-10ng/ml. The mean recoveries of alprazolam and α-hydroxyalprazolam added to plasma were 98.05±5.75% and 96.25±5.70%, respectively, with the relative standard deviation of less than 7.8 and 10.6%. The method is applicable to drug monitoring of alprazolam and α-hydroxyalprazolam level in plasma of healthy volunteers and patients treated with alprazolam.