The changes in FEV1 and in specific conductance induced by 200 micrograms oxitropium bromide given as pressurized aerosol were measured at 8 time intervals during 7 hours after inhalation in a group of 19 patients with reversible broncho-obstruction. The working of the drug was compared to the functional values observed at the same time intervals after placebo, 40 micrograms ipratropium bromide and 400 micrograms fenoterol. Both oxitropium and ipratropium were definitely and significantly superior to placebo at all time intervals. Oxitropium was superior to ipratropium at the 7th hour. At this time interval the difference was significant At the 7th hour oxitropium gave higher mean results than fenoterol, but this difference was not significant. The drug was also compared to its competitors regarding its subjective and cardiovascular tolerance. No unfavourable side-effects were observed.