The fixed-combination metered aerosol lK6 (fenoterol 0.05 mg/puff, ipratropium bromide 0.02 mg/puff--Berodual, Boehringer-Ingelheim Ltd., Ridgefield, Conn.) was administered to 12 children (8 boys, 4 girls) aged 3 1/2 to 6 2/12 years who had extrinsic bronchial asthma. Three forms of administration, each with a different site of action, were compared: Two puffs during inspiration. Probable site of action: oral cavity, pharynx, larynx, trachea, and bronchi. Two puffs using an inhalational aid during inspiration. Probable site of action: pharynx, larynx, trachea, and bronchi. Two puffs in the breathing interval after deep inspiration. Probable site of action: oral cavity and pharynx. The resistance of the respiratory system (Rrs) was measured using oscillometry for up to 360 minutes after administration. A significant decrease of the median resistance was found with all three forms of administration. The changes were Form 1-48% of baseline after 120 minutes; Form 2-47.9% of baseline after 60 minutes; Form 3-44.4% of baseline after 30 minutes. The greatest decrease was observed with form 1. The study indicates that significant bronchodilation was achieved in small children using the combination of fenoterol and ipratropium bromide administered by metered aerosol even when inhalation and the release of the puff were not synchronized. A significant bronchodilator effect was also observed in cases of severe bronchial obstruction in which transport of the active ingredients to the lower airways could not be sufficiently guaranteed.