The pharmacokinetics of ibuprofen enantiomers were studied in rats after intravenous and oral administration of ibuprofen arginate by means of a chiral HPLC method.  The pharmacokinetics of ibuprofen was stereoselective after intravenous and oral administration of ibuprofen arginate.  The pharmacokinetic stereoselectivity was higher after oral administration than that after intravenous administration.  The systematic (R)-(−)-to-(S)-(+) inversion might be more important than the presystematic one in the stereoselective pharmacokinetics after oral administration.  Oral administration of ibuprofen arginate resulted in a very rapid absorption of (S)-(+)-ibuprofen (eutomer), and the absolute bioavailabilities of (S)-(+)-ibuprofen and (R)-(−)-ibuprofen were about 100% and 80%, respectively.  Based on the systemic exposure of (S)-(+)-ibuprofen, it could be concluded that the pharmacological actions might be similar when ibuprofen arginate was given orally and intravenously, except some differences in the onset of action.