We performed a randomized, double-blind, placebo-controlled cross-over study with two different concentrations of ipratropium bromide (Atrovent®) nasal spray to evaluate its onset and duration of inhibition. Twenty-four subjects with perennial rhinitis participated in the trial. Fifteen minutes to 12 hours after administration of ipratropium bromide (42 or 168 μg/nostril) or placebo nasal spray, methacholine challenges were performed and nasal secretion weights measured. After placebo administration the effect of methacholine remained unchanged over the 12-h-period. Both the 42 and 168 μg/nostril doses significantly inhibited the nasal hypersecretions induced by methacholine challenge within 15 min of treatment (P < 0.05). The 168 μg dose of ipratropium bromide continued to significantly reduce secretion weights through 6 hours, but the effectiveness of the 42 μg dose disappeared within 3 h. In addition to having a longer duration, the 168 μg/nostril dose produced approximately twice the inhibitory effect of the 42 μg dose.