A sensitive and specific method was developed for quantification of alprazolam and its two metabolites 4-hydroxyalprazolam and alpha-hydroxyalprazolam in plasma. The work up procedure was solid phase extraction. Liquid chromatography-mass spectrometry (LC-MS) was used for separation, detection and quantification of the analytes. The limit of quantitation (LOQ) was 0.05 ng/mL for alprazolam and the two metabolites. The extraction recovery was more than 82% for alprazolam and its metabolites. The within- and between-assay coefficients of variation were in the range of 1.9-17.9%. The method was used for determination of the pharmacokinetics parameters of alprazolam and its two metabolites in healthy Caucasian subjects who ingested 1mg of alprazolam.