The objective of the present study was to investigate the in vivo pharmacokinetics of huperzine A in healthy human volunteers. Twelve subjects (M 6, F 6; age ranged from 20-25 years) participated in the study. Huperzine A was administered in tablet form at a single dose of 0.4 mg. Following oral administration, the presence of huperzine A started to appear in the plasma at 5-10 min, and reached the peak concentrations with a Cmax of 2.59 +/- 0.37 ng/ml at 58.33 +/- 3.89 min (time to reach peak level, Tmax. The area under plasma vs time curve (AUC(0-t)) and the area under plasma from zero to infinity (AUC(0-infinity) for huperzine A were found to be 1986.96 +/- 164.57 microg/l.min and 2450.34 +/- 233.32 microg/l.min, respectively. The results of this study indicated that the pharmacokinetics of huperzine A conformed to a two-compartmental open model. The mean values of alpha and the beta half-life were 21.13 +/- 7.28 min and 716.25 +/- 130.18 min respectively, and showed a biphasic profile with rapid distribution followed by a slower elimination rate.