A high-performance liquid chromatographic assay method for the quantification of OPC-18790 enantiomers in human plasma and urine is described. A human plasma or urine was extracted with organic solvent under alkaline conditions following the addition of internal standard. The enantiomers and internal standard were then derivatized by reaction with the chiral reagent GITC (2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl isothiocyanate), followed by octadecylsilica chromatographic separation of the diastereomeric products. The mobile phase consisted of acetonitrile-water (41:59). The fluorescence of the eluate was monitored at 355/405 nm. The lowest quantification limit of each enantiomer was 10 ng/ml in plasma and 0.1 micrograms/ml in urine. Both intra- and inter-day coefficients of variation were below 10%. The assay is sensitive, specific and applicable for stereoselective pharmacokinetic studies in human.