The efficacy and safety of a novel fenoterol/ipratropium bromide metered-dose inhaler (MDI) formulated with a non-chlorinated propellant, HFA134a, has been compared with placebo and the conventional chlorofluorocarbon (CFC)-containing fenoterol/ipratropium bromide inhaler (Berodual) in asthmatic patients. Fifty-two patients were enrolled in two centres. The fenoterol/ ipratropium bromide treatment produced significantly (P < 0.0001) greater bronchodilatation than placebo. There were no significant differences between the mean peak and average forced expiratory volume in the first second (FEV1) for patients receiving 2 puffs of the fenoterol/ipratropium bromide HFA134a inhaler and the conventional CFC inhaler. In addition, time to onset and duration of efficacy were comparable for these two treatments. None of the patients showed a fall of > or = 15% in baseline FEV1 or needed rescue medication within 30 min after inhalation of the test drug. No paradoxical bronchoconstriction was observed as measured by sGaw. The two inhaler formulations were well tolerated. A taste-related complaint, lasting for a few minutes after inhalation, was reported by a higher proportion of patients who inhaled the HFA134a formulation, mainly by patients selected in one of the two centres. In conclusion, a dose of 100 micrograms fenoterol/40 micrograms ipratropium bromide inhaled from a MDI containing HFA134a propellant is safe and provides effective bronchodilatation of equivalent degree, onset and duration of action to the same dose from the conventional CFC formulation.