Postexertional wheezing is an important clinical sign of nonspecific airway hyperreactivity. We have studied wheezing after exercise in 6 asthmatic subjects, 13 to 20 yr of age, using spectral analysis of recorded tracheal sounds. Automated spectral characterization was used to measure wheezing as a proportion of respiratory time. Anticholinergic treatment with ipratropium bromide (Atrovent) was compared with placebo to investigate effects on postexertional wheezing, and pulmonary function was compared with the result of respiratory sound analysis. Atrovent did not abolish exercise-induced bronchospasm but improved preexercise lung function and thereby caused a parallel upward shift in the response curves. Wheezing after Atrovent was significantly less, later in onset, and mainly expiratory at 20 min after exercise. Wheezing as a percentage of total respiratory time correlated well with FEV1, Vmax50, and SGaw. Analysis of respiratory sounds and automated quantification of wheezing may be a useful complementary test of bronchial obstruction in asthma.