The dose-response relationships of a combination of the selective beta adrenergic agonist, fenoterol, and the synthetic anticholinergic drug, ipratropium bromide, were studied. In an open cross-over assessment, 20 patients with evidence of reversible airways obstruction inhaled 2, 4, 6 or 8 puffs from a metered dose inhaler, containing 100 micrograms fenoterol and 40 micrograms ipratropium bromide per puff, administered according to a randomization schedule, on four non-consecutive days. Before, and at intervals up to eight hours after inhalation FEV1, FVC, pulse and blood pressure were measured. Immediate and prolonged bronchodilatation followed each dose. The overall analysis of the FEV1, and FVC showed little difference between 2, 4 and 6 puffs. The highest dose, 8 puffs, was more effective, but associated with an increased incidence of side effects.