Airway remodeling in asthma refers to a collection of chronic structural changes including subepithelial fibrosis, airway smooth muscle hypertrophy/hyperplasia, and possibly angiogenesis. The mechanisms leading to remodeling are not well defined. One molecule of possible relevance is basic fibroblast growth factor (bFGF), which is a potent mitogen for fibro-blasts, airway smooth muscle cells, and endothelial cells. To test the hypothesis that bFGF expression is increased in asthma, we measured levels of the growth factor in bronchoalveolar lavage (BAL) fluid. Basally, BAL fluid bFGF concentrations were significantly higher in subjects with atopic asthma than in control subjects without asthma (median 0.22 vs 0.06 pg/mL, P = .003). The effect of acute allergen exposure was examined with a segmental bronchoprovocation model in a separate group of subjects with atopic asthma. Ten minutes after segmental bronchoprovocation there was a 5-fold increase in bFGF levels in BAL fluid recovered from allergen-challenged sites compared with control saline-challenged sites (1.52 vs 0.30 pg/mL, P < .002). We conclude that basal levels of BAL fluid bFGF are increased in atopic asthma and that a further increase occurs in response to acute allergen exposure. These findings lend support to the hypothesis that bFGF is implicated in airway remodeling in asthma.