Airway S-nitrosothiols (SNOs) are naturally occurring bronchodilators. SNOs, nitrate, and nitrite were measured in bronchoalveolar lavage fluid of 23 patients with cystic fibrosis (CF) and mild pulmonary disease (aged 6-16 years) and 13 healthy children (aged 8-15 years). Concentrations of SNOs were decreased in the lower airways of patients with CF and mild pulmonary disease (median, range: 0, 0-320 nmol/L vs 80, 0-970 nmol/L) despite normal levels of the inert nitric oxide metabolites nitrate and nitrite (mean +/- SEM: 3.7 +/- 0.5 micromol/L vs 4.8 +/- 0.9 micromol/L). S-nitrosolation- mediated bioreactivities may be impaired by depletion of the CF airway SNO reservoir.