Asthma is associated with increased expression of inflammatory proteins including cytokines, enzymes, and adhesion molecules. Induction of many of the genes for these proteins is regulated by the transcription factor, nuclear factor- κ B (NF- κ B). We therefore examined whether airway cells from patients with asthma show increased activation of NF- κ B. Nuclear proteins were extracted from cells of induced sputum and from bronchial biopsies of normal subjects and patients with asthma. NF- κ B-binding to its consensus DNA binding site, as investigated with ³²P-labeled oligonucleotides and electrophoretic-mobility-shift assay, showed a 2.5-fold increase (p < 0.003) in NF- κ B–DNA binding in induced sputum of asthma patients. Nuclear staining, representing activated NF- κ B, was observed in macrophages of induced sputum. Immunohistochemical examination of bronchial biopsy specimens with an antibody to p65, a constituent of NF- κ B, showed more airway epithelial cells with nuclear staining in asthma patients (45.1 ± 7.2% versus 20.7 ± 3.9%; n = 9; p < 0.01), and a 2.5-fold greater number of cells with cytoplasmic staining in the mucosal region (p < 0.05). Pooled nuclear extracts of bronchial biopsy specimens from asthma patients showed a 44% greater level of NF- κ B–DNA binding. Activation of NF- κ B may be the basis for increased expression of many inflammatory genes and for the perpetuation of chronic airway inflammation in asthma.