Cystic Fibrosis is characterized by prolonged and excessive inflammatory responses in the lung and increased activation of NF-B. Parthenolide is a sesquiterpene lactone derived from the plant feverfew, which has been used in folk medicine for anti-inflammatory activity. Several studies suggest that this compound inhibits the NF-B pathway but the exact site is controversial. We hypothesized that parthenolide might ameliorate the excessive inflammatory response in CF models by inhibiting activation of NF-B. This was tested in vitro, using two pairs of cell lines with defective vs normal CFTR (antisense/sense transfected 16 HBE and IB-3/S9), and in vivo, using CFTR-KO mice. All cell lines were pretreated with parthenolide and then stimulated with IL-1 and/or TNF. Parthenolide significantly inhibited IL-8 secretion induced by these cytokines and prevented NF-B activation, IB degradation and IB Kinase complex activity. CFTR-KO and WT mice were pretreated with parthenolide or vehicle alone then challenged intra-tracheally with LPS. BAL was performed 3, 6 and 8 h later. Parthenolide pretreatment inhibited PMN influx, cytokine and chemokine production. This was also associated with inhibition of IB degradation and NF-B activation. We thus conclude that parthenolide inhibits IB Kinase, resulting in stabilization of cytoplasmic IB, which in turn leads to inhibition of NF-B translocation and attenuation of subsequent inflammatory responses. IB Kinase may be a good target, and parthenolide and/or feverfew might be promising treatments for the excessive inflammation in CF.