We studied the bronchodilator and protective potency of inhaled ipratropium bromide in 33 patients with mild bronchial asthma. Patients were divided into 3 groups with similar baseline lung function and similar degrees of bronchial hyperresponsiveness to participate in the methacholine (study I, n = 9), histamine (study II, n = 9), or exercise challenge tests (study III, n = 18). At each session, 80 micrograms ipratropium bromide or placebo were inhaled in a double-blind randomized fashion. After ipratropium bromide, the mean specific airway resistance (SRaw) decreased from 10.4 to 4.9 (study I, p less than 0.01), 9.3 to 5.4 (study II, p less than 0.05), or 7.8 to 5.1 cm H2O.s (study III, p less than 0.01), respectively. Mean methacholine provocation concentrations necessary to increase SRaw by 100% were 0.43 after placebo and 8.60 mg/ml after ipratropium bromide (p less than 0.01), the respective values after histamine challenges were 1.32 mg/ml after placebo and 2.25 mg/ml after ipratropium bromide (p less than 0.01). In the exercise challenges, the individual responses varied largely with a mean maximum percent increase in SRaw of 231% after placebo and 173% after ipratropium bromide pretreatment (p less than 0.05). Therefore, ipratropium bromide offers bronchodilation and protection against a variety of stimuli and should more often be considered as an effective and safe drug for asthma treatment.