We have studied cough and bronchial constriction induced by inhaling citric acid in 15 smokers with baseline airflow obstruction, in 13 occasional smokers and 13 non smokers. The threshold for cough was significantly higher in occasional smokers in relation to smokers and non smokers. Citric acid produced the same degree of bronchial constriction at the same time in smokers and occasional smokers: the maximum fall in forced expired volume (FEV1-VEMS) was recorded five seconds after inhalation of the citric acid (dose threshold) and there was no significant difference between the two groups. In the non smokers, the maximum fall in VEMS was recorded twenty seconds after inhalation of the citric acid and was significantly less in relation to that of the smokers and occasional smokers. In the smokers the degree of smoking could influence the fall of VEMS (% predicted). Cough and bronchial constriction after the inhalation of citric acid are probably related to different physiological mechanisms and are linked to the history of smoking.