A stereoselective reversed-phase HPLC assay to determine S-(-) and R-(+) enantiomers of esmolol in human plasma was developed. The method involved liquid–liquid extraction of esmolol from human plasma, using S-(-)-propranolol as the internal standard, and employed 2,3,4,6-tetra-O-acetyl-h-D-glucopyranosyl isothiocyanate as a pre-column chiral derivatization reagent. The derivatized products were separated on a 5-Am reversed-phase C18 column with a mixture of acetonitrile/0.02mol/L phosphate buffer (pH 4.5) (55:45, v/v) as mobile phase. The detection of esmolol derivatives was made at k=224nm with UV detector. The assay was linear from 0.035 to 12Ag/ml for each enantiomer. The analytical method afforded average recoveries of 94.8% and 95.5% for S-(-)-and R-(+)-esmolol, respectively. For each enantiomer, the limit of detection was 0.003Ag/ml and the limit of quantification for the method was 0.035Ag/ml (RSD<14%). The reproducibility of the assay was satisfactory.