SUMMARY We investigated inhaled citric acid-induced cough and bronchial obstruction in 15 smokers without chronic airflow limitation, 13 occasional smokers and 9 non smokers. Cough threshold was significantly higher in occasional smokers in comparison to smokers and non smokers. Citric acid-induced bronchial obstruction had a similar pattern in smokers and occasionaI smokers: the maximal fall of FEV1 took place at 5 seconds post-inhalation of citric acid and maximal fall of FEV1 was statistically significant between the two groups. In non smokers, the maximal fall of FEV1 was significantly less than in smokers and occasional smokers. In smokers, the degree of tobacco consumption seems to influence the percent fall of FEV1 (r = 0.48, p < 0.10). It is concluded that cough and bronchial obstruction to noxious agents such as citric acid are based upon different physiological mechanisms and they depend on smoking history of the subject. Pneumon 1999, 12 (3): 189-195