This report describes a highly sensitive capillary gas chromatographic/mass spectrometric procedure for the quantification of alprazolam in human plasma. Alprazolam was extracted from plasma at basic pH with benzeneisoamyl alcohol (98:2, v/v) and analysed directly without any derivatization. Triazolam, also a triazolobenzodiazepine derivative, was used as an internal standard because its extraction characteristics were similar to alprazolam. High sensitivity was achieved by negative ion chemical ionization and selected ion monitoring for alprazolam (m/z 308) and triazolam (m/z 306). The within-day coefficient of variation of the method over the concentration range 1.0-20 ng alprazolam per ml of plasma was 5.5%.