The efficacies of inhaled doses of fenoterol 200 micrograms, ipratropium bromide 40 micrograms and their combination (200 + 40 micrograms) were compared in a double-blind, placebo-controlled cross-over study in 24 adult patients with stable asthma bronchiale. The tests were performed during 4 consecutive days. The change in bronchial obstruction was assessed by means of spirometry [forced expiratory volume in 1 s (FEV 1.0), forced vital capacity (FVC), peak expiratory flow (PEF)] and body plethysmography [thoracic gas volume (TGV), airway resistance (Raw)] measurements. The values of FEV% and specific airway conductance (SGaw) were calculated. The frequency of side-effects was recorded. During the treatment with the combination of ipratropium bromide and fenoterol the change in the mean SGaw differed highly significantly (p less than 0.001) from placebo in the initial bronchodilator response and at 3, 4 and 5 h. With fenoterol, compared to placebo, a highly significant difference in bronchodilator effect lasted for 4 h, with ipratropium bromide for 3 h. Similarly, a highly significant difference measured with FEV 1.0 during the medication with the combination of ipratropium bromide and fenoterol lasted for 4 h, with fenoterol alone for 2 h, and with ipratropium alone for 1 h. The most harmful side-effect in this group of asthmatics proved to be muscular tremor, caused most often by the combination of ipratropium bromide and fenoterol. The findings of this study suggest that the combination of ipratropium bromide and fenoterol gives a stronger bronchodilatation and a more prolonged effect in asthmatics than ipratropium bromide or fenoterol alone.(ABSTRACT TRUNCATED AT 250 WORDS)