A simple reverse-phase high-performance liquid chromatographic (HPLC) assay for the measurement of amiodarone and its metabolite, desethylamiodarone in the serum was established. The ODS-2 column was used and the absorbance of the effluent from the column at 254 nm was measured. The standard curves for amiodarone and desethylamiodarone were linear up to 5μg/ml. The coefficent of variation (CV) was within 10% at a concentration of 100 ng/ml, and the CV of the intra-and interday variation was within 10% at concentrations of 0.25, 0.5 and 1μg/ml, respectively. These results suggest that the limit of detection is 100 ng/ml for amiodarone and desethylamiodarone, and this assay is thus considered to be a reliable method in clinical practice. On the other hand, the serum amiodarone and desethylamiodarone concentrations were measured in 10 inpatients who received amiodarone for at least 1 month. No significant correlation was observed between the doses and serum drug concentrations. There findings therefore suggest that TDM (Therapeutic Drug Monitoring) should be performed on anyone taking amiodarone.