20 (R,S)-Ginsenoside-Rg2, an anti-shock agent, is prescribed as a racemate. To analyze simultaneously the enantiomers of 20 (R)-ginsenoside-Rg2 and 20 (S)-ginsenoside-Rg2 in plasma, a simple and reproducible high-performance liquid chromatographic (HPLC) method has been developed. The enantiomeric separation and determination were successfully achieved using a Diamonsil ODS C18 reversed-phase column (5 microm, 250 mm x 4.6 mm) with an RP18 (5 microm) guard column and a mobile phase of MeOH-aq. 4% H3PO4 (65:35, v/v, pH 5.1) with UV detection at 203 nm. Both enantiomers, 20 (R)-ginsenoside-Rg2 and 20 (S)-ginsenoside-Rg2, were well separated at 14.5 min and 13.6 min, respectively. The linear ranges of the standard curves were 2.0-250 microg/ml. The intra- and inter-day precision (R.S.D.) were <or=1.59% and <or=0.54% and the mean extraction recoveries were 95.8% and 96.5% for 20 (R)-ginsenoside-Rg2 and 20 (S)-ginsenoside-Rg2 in rat plasma, respectively. The limits of detection and quantification were 2.0 microg/ml and 7.8 microg/ml (S/N=3:1) for 20 (R)-ginsenoside-Rg2, and 2.0 microg/ml and 3.9 microg/ml (S/N=3:1) for 20 (S)-ginsenoside-Rg2, respectively. This validated method was applicable to pharmacokinetic studies in rat plasma after intravenous administration of 20 (R,S)-ginsenoside-Rg2. A pharmacokinetic study in rat plasma indicated that the enantiomers were rapidly absorbed and eliminated. These assay results are necessary for the evaluation of the metabolism of ginsenoside-Rg2 in vivo.