Anticholinergic agents have been widely used in the management of asthma. The use of scopolamine has been limited by significant side effects. Transdermal delivery of scopolamine (TS) has, however, been used successfully for the prevention of motion sickness. The purpose of this study was to determine if TS would decrease methacholine-induced bronchospasm in a group of subjects with mild asthma. Bronchoprovocational challenges with inhaled methacholine were performed on three separate occasions in 10 male subjects who each had a past history of asthma. After a baseline challenge, each subject received, in a double-blinded fashion, either a placebo patch or TS patch. The challenge was then repeated after at least 36 hours, and the alternate patch was then dispensed. The provocative dose producing a fall in FEV1 by 20% from baseline was then calculated by linear regression analysis. No significant change in baseline pulmonary function was noted with placebo patch or TS. With the use of TS, there was a small but significant increase in the provocative dose producing a fall in FEV1 by 20% from baseline for the group (p less than 0.05). In conclusion, we were able to demonstrate that a TS patch worn for a short period of time, can significantly decrease airway reactivity to methacholine in some patients with hyperactive airways.