The present study aimed at delineating the mechanisms underlying the adverse response to hypertonic saline inhalation in patients with chronic obstructive pulmonary disease (COPD). Twenty patients (age, 48-70 yr; FEV(1), 29-58 %pred) inhaled, on two different days in randomized order, 200 microg salbutamol from an MDI and 20 min later either 0.9% or 3% saline from an ultrasonic nebulizer for a maximum of four consecutive 5-min periods. Forced expiratory (FEV(1)) and inspiratory (FIV(1)) volumes, inspiratory capacity (IC), intrathoracic gas volume (ITGV), and specific airway resistance (SRaw) were measured. Significant changes occurred in FEV(1), FIV(1), IC, ITGV, and SRaw with both concentrations (p < 0.05, each) and effects were stronger with 3% as compared with 0.9% saline (p < 0.05, each). The increase in dyspnea was associated with the changes in FIV(1), FEV(1), IC, and ITGV, in contrast to its decrease during bronchodilation, where only FIV(1) was important. Sputum analysis showed elevated concentrations of histamine after 3% as compared with 0.9% saline. These data indicate that the adverse lung function response to hypertonic saline is common in patients with moderate to severe COPD, involves both bronchoconstriction and lung hyperinflation, and could be mediated, at least partially, through activation of mast cells.