Topical application of the anti-cholinergic drug ipratropium bromide is used for the treatment of rhinorrhoea. As the commercially-available pressurized aerosols are now largely being replaced by aqueous pump sprays, not containing CFC gases, we have compared these two types of sprays in a time-effect study of 20 normal persons, using the secretory response to nasal methacholine challenge as the effect parameter. Pre-treatment has been given as a single dose of 80 mg of ipratropium bromide, and 24 mg methacholine was used for challenge. The pressurized aerosol reduces rhinorrhoea with 60% (p < 0.05) and the effect lasts for at least 8 h. The corresponding value for the aqueous pump spray is 40% (p < 0.05) and the effect lasts for less than 4 h. The differences between the two sprays is significant 30 min, 1, 2 and 4 h after medication (p < 0.05). This finding is unexpected and we cannot offer a satisfactory explanation. The result indicates that changes in dosing and dose-frequency of ipratropium bromide may be necessary when patients are transferred from a pressurized spray to an aqueous pump spray.