A stereoselective reversed-phase liquid chromatographic method for the determination of compounds LY300502 and LY300503 (enantiomers of LY191704) in rat and dog plasma was developed. The assay involved extraction of the compounds using a strong cation-exchange solid-phase extraction column, from which the compounds are eluted with 1% of 1 M HCI in methanol. The enantiomers were separated on a Daicel Chiralcel OD-R column. The mobile phase consisted of water-acetonitrile-methanol (50:40:10, v/v) at a flow-rate of 0.3 ml/min. UV detection was achieved at 220 nm. The disposition of the enantiomers of LY191704 in rats and dogs was found to be stereoselective and species specific.