A high-performance liquid chromatographic procedure, including sample pretreatment, is presented for the analysis of the experimental antitumour drug vintriptol in plasma. The sample pretreatment involved liquid-liquid extraction of the buffered (pH 3) sample with chloroform. Vinblastine was used as internal standard. Separation was achieved on a Hypersil ODS (5 microns) column with a mobile phase of acetonitrile-phosphate buffer. Electrochemical detection (at +0.70 V) was used, giving a detection limit of 2 micrograms/l. The applicability of the assay was demonstrated in a pharmacokinetic study with eight cancer patients who received 45 or 50 mg/m2 vintriptol in a phase I study. A three-compartment model was used to fit the plasma concentration-time curves. Pharmacokinetic parameters are presented.