Furin, a human subtilisin-related proprotein convertase, is the most important pharmaceutical target because it plays a vital role in development of numerous disease processes. To identify a new class of small non-peptide inhibitors of furin we performed a study of several flavonoids and some natural products. Glycosylated flavonoids: rutin, naringin, baikalin and methylhesperidin were shown to inhibit furin at pH 7.2 reversibly and competitively with Ki- 80-200 microM. The Ki values were derived from Dixon and/or Eadie-Hofstee plots using fluorogenic substrate Boc-Arg-Val-Arg-Arg-AMC. Although studied flavonoids display only a temperate furin inhibition, they may serve as a great potential for the future development of more potent non-peptide inhibitors against furin.