Cystic fibrosis (CF) is characterized by airway inflammation and chronic bacterial lung infection, most commonly with Pseudomonas aeruginosa, an opportunistic human pathogen. Despite the persistent airway inflammation observed in patients with CF, although phagocyte inducible nitric oxide synthase (iNOS) production is upregulated, expression of iNOS in the respiratory epithelium is markedly reduced. Given the antimicrobial action of NO, this may contribute to the chronic airway infection of this disease. To define the role of epithelium-derived NO in airway defense against P. aeruginosa, we infected differentiated human bronchial epithelial cells derived from a patient with CF (CFBE41o- cells) with different strains of this pathogen at low multiplicities of infection. Using cells transfected with human iNOS cDNA, we studied the effect of NO on P. aeruginosa replication, adherence, and internalization. P. aeruginosa adherence to iNOS-expressing cells was reduced by 44 to 72% (P = 0.02) compared with control values. Absolute P. aeruginosa uptake into these cells was reduced by 44%, but uptake expressed as a percentage of adherent bacteria did not differ from the control uptake. Survival of P. aeruginosa within iNOS-expressing cells was reduced at late times postinfection (P = 0.034). NO production did not alter host cell viability. NO production reduced P. aeruginosa adherence to human bronchial epithelial cells and enhanced killing of internalized bacteria, suggesting that a lack of epithelial iNOS in patients with CF may contribute to P. aeruginosa infection and colonization.