A rapid and sensitive reversed-phase high performance liquid chromatographic method for the quantitation of five furanocoumarins (bergaptol, psoralen, bergapten, 6',7'-dihydroxybergamottin, and bergamottin) is developed and validated. HPLC analysis of these five furanocoumarins is performed on a reversed-phase Inertsil ODS-2 column with a particle size of 5 pi Using only water and acetonitrile as solvents, good separation, good precision, and high accuracy are obtained for the analysis of furanocoumarin components. This method is validated and applied to analyze the composition of five furanocoumarins in four citrus fruit juices (grapefruit, pomelo I, pomelo II, and shaddock) and ten Chinese herbal medicines (Bai-Zhi, Qiang-Huo, Du-Huo, Fang-Feng, Dang-Gui, Huang-Qin, Gan-Cao, Chen-Pi, Ge-Gen, and Yin-Chen-Hao) prepared by water decoction or an alcohol infusion. Results show that four of the five furanocoumarins (but not bergapten) are detected in grapefruit, pomelo I, and pomelo II, and the highest amount of these components is found in grapefruit juice. In the ten Chinese herbal medicines, the five furanocoumarins are not detected in Ge-Gen or Yin-Chen-Hao. The remaining herbs contain various compositions and amounts of furanocoumarins. In general, Chinese herbal medicines prepared by the 40% ethanol infusion contain larger amounts of furanocoumarins than those prepared by hot water decoction.