A simple, rapid and sensitive assay for the quantitation of dipyridamole in human plasma has been developed using a reversed-phase C18 microbore HPLC column. Dipyridamole and the internal standard (propranolol) were separated from the plasma by reversed-phase liquid chromatog. following a direct plasma protein precipitation For sample anal. 50 μL of the internal standard (propranolol 125 μg/mL) and 50 μL of perchloric acid (60% w/v) were added to the 500 μL plasma. After brief vortex and centrifugation, the supernatant (100 μL) was injected onto the column. Chromatog. was carried on a 5 μm ODS Hypersil C18 microbore column (2 mm I.D. × 10 cm) using an acetonitrile-water (48:52 volume/volume) mobile phase containing 20 mM Na2HPO4 and 50 mM sodium dodecyl sulfate adjusted to pH 2. The eluant was monitored at 305 nm. The run time for a plasma sample was less than 12 min. The intra- and inter-assay coefficients of variation were less than 9%. The lowest limit of detection for dipyridamole was 0.05 μg/mL (50 ng/mL). The specificity, sensitivity and reproducibility of the procedure are adequate and suitable for the clin. pharmacokinetic, bioavailability and therapeutic drug monitoring studies.