The pharmacokinetics and tolerance of pantoprazole were investigated after single (20, 40, 80, and 120 mg) and multiple (80 mg once a day for 7 days) oral administration as enteric-coated tablet formulation to healthy male Japanese volunteers. Pantoprazole was well tolerated with no serious adverse events at all doses. Pantoprazole was rapidly absorbed in the fasted state. The mean maximum concentration in serum (Cmax) ranged from 1.77-9.25 micrograms/ml for the 20-120 mg dose and the mean time to reach Cmax (tmax) ranged from 1.92-2.42 h. The half-life (t1/2) ranged from 0.74-1.16 h. A good linear correlation was found between the administered doses (20-120 mg) and the resulting area under the concentration-time curve (AUC) and Cmax with the correlation coefficients of 0.9088 and 0.9263, respectively. Within 24 h, pantoprazole was excreted into urine as the unchanged drug to a negligible extent. In the multiple dose study, 2 apparent poor metabolizers (PMs) of pantoprazole were observed. The means of Cmax, AUC and t1/2 for these 2 PMs were 1.6, 6.7, and 6.8 times higher than those of the extensive metabolizers (EMs). The pharmacokinetic parameters such as Cmax, AUC, and t1/2 after the 7th oral dose were not significantly different from those after the 1st dose both in the PMs and the EMs, which indicated that there was virtually no drug accumulation.