The pathophysiology of cystic fibrosis (CF) inflammatory lung disease is not well understood. CF airway epithelial cells respond to inflammatory stimuli with increased production of proinflammatory cytokines as a result of increased NF-κB activation. Peroxisome proliferator-activated receptor-γ (PPARγ) inhibits NF-κB activity and is reported to be reduced in CF. If PPARγ participates in regulatory dysfunction in the CF lung, perhaps PPARγ ligands might be useful therapeutically. Cell models of CF airway epithelium were used to evaluate PPARγ expression and binding to NF-κB at basal and under conditions of inflammatory stimulation by Pseudomonas aeruginosa or TNFα/IL-1β. An animal model of CF was used to evaluate the potential of PPARγ agonists as therapeutic agents in vivo. In vitro, PPARγ agonists reduced IL-8 and MMP-9 release from airway epithelial cells in response to PAO1 or TNFα/IL-1β stimulation. Less NF-κB bound to PPARγ in CF than normal cells, in two different assays; PPARγ agonists abrogated this reduction. PPARγ bound less to its target DNA sequence in CF cells. To test the importance of the reported PPARγ inactivation by phosphorylation, we observed that inhibitors of ERK, but not JNK, were synergistic with PPARγ agonists in reducing IL-8 secretion. In vivo, administration of PPARγ agonists reduced airway inflammation in response to acute infection with P. aeruginosa in CF, but not wild-type, mice. In summary, PPARγ inhibits the inflammatory response in CF, at least in part by interaction with NF-κB in airway epithelial cells. PPARγ agonists may be therapeutic in CF.