The effect of 4% lidocaine inhalation was studied in a single-blind fashion in 18 patients with chronic stable asthma. Inhalation of normal saline solution was used as placebo. None of the parameters except flow rate at 50% of vital capacity (V50) showed any statistically significant change from baseline values. V50 at 15 min was significantly lower (p less than 0.05) after 4% lidocaine inhalation. Considering more than 10% change from the baseline value as significant, 8 of 15 patients showed decrease in airway resistance (Raw) and 7 of the 15 patients showed an increase in specific airway conductance (SGaw) after 15 min of inhalation. However, V50 (8/18 patients), flow rate at 25% vital capacity [V25 (6/15 patients], and forced expiratory flow rate at 25-75% of the vital capacity (FEF25-75) (5/15 patients) showed a decrease after 15 min of 4% lidocaine inhalation. No change in pulmonary function was noted after 30 min of lidocaine inhalation. It is concluded from this study that lidocaine produces a small bronchodilatory effect on the large airways and a bronchoconstrictor effect on the small airways after 15 min of inhalation, but this effect is not statistically significant. It can be safely used as topical agent for bronchoscopy in patients with bronchial asthma.