The pulmonary surfactant is thought to be important in the stability of the small airways. In this study, we conducted a double-blind, placebo-controlled trial to determine whether surfactant inhalation has a therapeutic effect in asthmatic attack. Eleven patients with asthmatic attack whose conditions were stable for at least six hours before the study were randomly assigned to placebo or surfactant inhalation. Respiratory function tests and blood gas analysis were performed before and 20 minutes after the treatment. After placebo administration, no significant change was observed from baseline in pulmonary functions. After surfactant administration (1 ml; 10 mg per milliliter), respiratory functions were markedly improved in all patients. The mean (+/- SE) change in the FVC, FEV1.0, MMF, delta N2 and PaO2 was, respectively, an increase of 11.7 +/- 1.3% (p less than 0.001), an increase of 27.3 +/- 4.4% (p less than 0.05), an increase of 33.3 +/- 4.7% (p less than 0.05), a decrease of 31 +/- 8.4% (p less than 0.05) and an increase of 13.4 +/- 0.8% (p less than 0.05). No difference was detected in PaCO2 after surfactant inhalation. This study indicates that airway surfactant is involved in the pathogenesis of bronchoobstruction of the patients with asthma.