Abstract: A reversed phase HPLC method to stereoselectively determine enantiomers of propafenone in human plasma has been developed. After extraction of 1 ml plasma with 3 ml of n-C₆H₁₄∶CH₂Cl₂∶2-C₃H₇OH (100∶50∶5, v/v) and dried under N₂, the enantiomers of propafenone were allowed to react with homochiral S(+)-1-(1-naphthyl) ethyl isocyanate (5.66 μg in 60 μl CH₂Cl₂) at RT for 30 min, to give the diastereomeric derivatives. Their separation was achieved using HPLC with a C₁₈-column and UV-detection (220 nm) and the enantiomeric ratios were measured. The concentrations of each enantiomer were then calculated using the enantiomeric ratios and the racemic propafenone concentrations previously measured. This method after validation procedures has been applied to the multisample analyses of a human pharmacokinetic study with 10 healthy volunteers after an oral dose of 300 mg propafenone hydrochloride.The method was shown to be sensitive (7.5 ng·ml^-1), convenient and reproducible.