Fifteen children who presented with chronic cough as an isolated manifestation of respiratory disease were evaluated for the presence of exercise-induced airway hyperreactivity. Pulmonary function tests using air and a helium/oxygen gas mixture were performed before exercise. Air curves alone were performed repeatedly after exercise. Eight subjects were also evaluated by spirometry and maximum expiratory flow volume curves before and after isoproterenol inhalation on a separate day. Ten subjects had normal pulmonary function tests at rest and five had isolated minor abnormalities. No significant changes in pulmonary function tests were recorded after inhalation of isoproterenol in the eight subjects studied. Following exercise, all 15 subjects demonstrated changes in pulmonary function tests which were similar to those seen in children with mild exercise-induced bronchospasm. After institution of theophylline, exercise-induced decreases in flow rates low in the vital capacity were blocked in all subjects; however, several subjects had persistent mild decreases in peak flow. Within six months of discontinuing the theophylline, cough recurred in 11 of the 15 subjects. Nine subjects were restudied after return of their cough. Exercise again resulted in decreased lung function. Reinstitution of theophylline eliminated the cough in these nine subjects. This study demonstrates that chronic cough in some children may be a manifestation of airway hyperreactivity. Both the cough and the reactivity can be blocked with theophylline.

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