A double-blind crossover placebo controlled study was performed on 20 patients with stable chronic asthma, in order to obtain dose response data to ipratropium bromide (40, 80, 200 micrograms) given by metered dose inhaler. The use of the 200 micrograms dose gave a significantly greater peak effect and duration of action than the recommended standard therapeutic dose of 40 micrograms. There were marked individual variations in response to higher doses. Maximum response detected by spirometry occurred within 24 hours of inhalation, thus patients likely to gain clinical benefit are readily identified. The higher dose was well tolerated by most patients and may have clinical application in the treatment of patients who do not respond to the standard dose regime.