Domperidone is currently used in Canada and Europe for the treatment of intestinal motility disorders as well as for its antiemetic properties. Recent drug metabolism studies have indicated that domperidone is a substrate of different subtypes of CYP3A family and consequently, the drug requires complete characterization of its metabolism for the identification of major drug-drug interactions. Therefore, the purpose of our studies was to develop a simple, sensitive and rapid HPLC assay for the determination of domperidone and its major metabolites. This assay had to be suitable for the conduct of in vitro drug metabolism study with human liver microsomes. Baseline resolution of internal standard, domperidone and three of its major metabolites was achieved in a run time of less than 15 min using an Ultrasphere ODS column (250 mm x 4.6 mm x 5 microM) and a mobile phase consisting of disodium citrate buffer (10 mM, pH 3.4):methanol:acetonitrile:trietylamine, 54.6:34.7:9.9:0.8 at a flow rate of 1.0 mL/min. Chromatographic separation was executed at room temperature. Quantification was performed by tandem fluorescence (excitation lambda=282 nm and emission lambda=328 nm) and ultraviolet detectors (lambda=254 nm for the quantification of encainide, internal standard). Calibration curves were constructed and showed linearity in the range of 0.1-20 micromol/L and 10-250 micromol/L. Intra- and interday coefficients of variation were less than 8% and 11%, respectively. Mean accuracy was 100.5+/-9.9% and limit of quantification was established at 0.06 micromol/L for domperidone and its metabolites. The assay allows estimation of enzymatic parameters (K(m) and V(max)) of domperidone for the formation of its various metabolites and sensitivity is sufficient for the conduct of inhibition studies with potent CYP3A inhibitors.