The comparison of pharmacokinetics of bifemelane hydrochloride (BFM) was studied in the young and the elderly. BFM (50mg) was administered orally after breakfast to young healthy subjects (male, N=8, mean age 21.1 years old, mean body weight 62.0kg) and to elderly patients (male N=8, female N=9, mean age 78.9 years old, mean body weight 44.4kg). Blood and urine samples were collected at 2, 4, 6, 8, 10, 12, 24hr and 0-8, 8-24hr, respectively to determine the plasma concentrations of BFM, M-2 (main metabolite of BFM) and the urinary concentrations of BFM, M-2, M-2 glucuronide. Plasma albumin (Alb) and α₁-acid glycoprotein (AAG) concentrations and creatinine clearance (CL_CR) were also determined in both groups. CL_CR in the elderly (52.9ml/min) was significantly low compared to the young (102.5ml/min). The lower concentration of Alb and higher concentration of AAG in the elderly were also observed. Plasma concentrations of BFM in the elderly were significantly higher (P<0.05-0.001) from 2 to 12hr after dosing. At 2 and 4hr, the t_max of BFM and the plasma concentrations of BFM (11.25, 9.18ng/ml) in the elderly were 3-4 fold higher than those (2.67, 3.11ng/ml) in the young. Plasma M-2 concentrations in the elderly were also higher than those in the young. BFM was not detected in urine in both groups; however, urinary excretion of M-2 and its glucuronide were shown to be delayed in the elderly. C_max of BFM in the elderly (13.41ng/ml) was about 4 times higher than that (3.21ng/ml) in the young. AUC of BFM in the elderly (74.26ng hr/ml) was significantly larger than that (20.24ng hr/ml) in the young. Prolonged t_1/2 of BFM in the elderly was shown. These results suggested that higher plasma concentrations of BFM or M-2 in the elderly might be mainly due to decreased hepatic metabolism (decreased first pass effect) of BFM.