A rapid, inexpensive and sensitive high-performance liquid chromatographic method for the quantitation of ibuprofen enantiomers from a variety of biological fluids is reported. This method uses a commercially available internal standard and has significantly less interference from endogenous co-extracted solutes than do previously reported methods. The method involves the acid extraction of drug and internal standard [(+/-)-fenoprofen] from the biological fluid with isooctane-isopropanol (95:5) followed by evaporation and derivatization with ethylchloroformate and R-(+)-alpha-phenylethylamine. Excellent linearity was observed between the peak-area ratio and enantiomer concentration (r > 0.99) over a concentration range of 0.25-50 micrograms/ml. This method is suitable for the quantitation of ibuprofen from single-dose pharmacokinetic studies involving either rats or humans.