The flavonoid content of Passiflora incarnata herba, which has been related to the pharmacological activity of drug, shows a great variability both qualitatively and quantitatively. Therefore the standardization of this herbal medicine is essential. As an alternative to HPLC methods, a quantitative TLC method has been validated. The separation conditions include: a single step extraction with methanol; the separation of the main flavonoids on RP-18 TLC-plate using a mobile phase containing H 3 PO 4 ; the direct densitometric determination at 355 nm without spray reagent; the use of only one commercially available standard, isovitexin. The method is rapid, reliable and requires no pre-purification steps; the selected chromatographic conditions allow a good separation of isovitexin from all other flavonoids so that it is possible to express separately the isovitexin content and the total flavonoid content expressed as isovitexin. The chromatograms show satisfactory separations of the flavonoids and are useful as fingerprints for further comparison between samples of different origin, or during extraction methods and stability tests.