OBJECTIVE The utility of an analysis of breath sounds as a non-invasive lung function test in children and adults has been studied. Analyzing specific breath sounds during methacholine inhalation challenge is useful for evaluating airway constriction in asthmatic patients. METHODS The study population included 57 children with atopic asthma (male: female = 38: 19; median age, 10 years [range, 5-16 years]). The breath sound spectrum was measured before a methacholine inhalation test, just after the methacholine inhalation challenge and after β2 agonist inhalation. The values of breath sound parameters were analyzed and the direct changes of the sound spectrum during methacholine inhalation challenge were evaluated. RESULTS The values of breath sound parameters, RPF75 and RPF50, were significantly decreased after methacholine inhalation (P < 0.001, p < 0.001, respectively), indicationg bronchoconstriction, and increased after β2 agonist inhalation (P < 0.001, p < 0.001, respectively), indicating bronchodilation. The high-pitch area of the sound spectrum curve around 1,500 Hz was significantly increased after methacholine inhalation (P < 0.001). The values returned to the baseline level after β2 agonist inhalation. CONCLUSIONS Bronchoconstriction by methacholine inhalation induced a reversible high-pitch sound. The assessment of changes in the high-pitch area of the breath sound spectrum may be useful for the detection of airway narrowing in asthmatic patients.