1. The plasma and urinary metabolite profiles of efonidipine hydrochloride, a new dihydropyridine calcium antagonist, have been examined in six healthy male volunteers after oral dosing. 2. Unchanged drug in plasma was determined by hplc-ms. Five metabolites in plasma and five metabolites and unchanged drug in urine were identified by hplc. 3. The main plasma metabolites were N-dephenylated-efonidipine and deaminated-efonidipine. 4. No significant amount of unchanged drug was excreted in urine. In the urine collected for 24 h after a oral dosing, 1.1% of the dose was excreted as deaminated-efonidipine, and 0.5% as a pyridine analogue of deaminated-efonidipine.