Various physical activities have been responsible for airway obstruction in asthmatic children.We report the resuits of 5min free running outdoors,5min bicycle ergometer physical load/2W/kg b.w./on lung function tests reflecting airway obstruction in asymptomatic asthmatic children,6 to 15 years old.The effects of forced expiration maneuver,inhalations of acetylcholine and histamine on induced airway obstruction were also studied in the same subjects.Maximum expiratory flow at 25% of VC was the most sensitive parameter in detecting the induced airway obstruction.Based on the latter parameter,airway obstruction following 5min free running outdoors was revealed in 80 - 100% of the patients.Mean percent reduction of the latter parameter varied from 60 to 80% of the initial value.The 5min bicycle ergometer exercise of about the same extent evoked much lower reduction/10%/of the latter parameter. The induced airway obstruction by 5min free running outdoors was prevented by a cloth face mask at running,inhalations of beta-2-mimetics,anticholinergic agent.The 5min, free running outdoors induced about the same extent of airflow limitation as a 3mg acetylcholine inhalation. We concluded that a 5min free running outdoors was as a most suitable test for an induced airway obstruction in our asthmatic children.