Alpinia pricei (Zingiberaceae) is a spicy herb indigenous to Taiwan. A potent anti-inflammatory compound, flavokawain B (FKB), was obtained from A. pricei. FKB significantly inhibited production of NO and PGE(2) in LPS-induced RAW 264.7 cells. Moreover, it also notably decreased the secretion of TNF-alpha. Expression of iNOS and COX-2 proteins was also inhibited by FKB in a dose-dependent manner. FKB blocked the nuclear translocation of NF-kappaB induced by LPS, which was associated with prevention IkappaB degradation, and subsequently decreased NF-kappaB protein levels in the nucleus. Similar anti-inflammatory activities of FKB were observed in an animal assay. NO concentrations in mouse serum rose dramatically from 3.2 to 28.8 microM after mice were challenged with LPS; however, preadministration of 200 mg/kg FKB reduced the NO concentration to 3.8 microM after challenge with LPS. Moreover, FKB strongly suppressed LPS-induced iNOS, COX-2, and NF-kappaB proteins expression in mouse liver.