We studied the effect of smoking cessation on airway reactivity. We recruited cigarette smokers who were attempting to stop smoking. Entry criteria required each subject to be smoking at least 10 cigarettes each day and report a chronic cough. Exclusion criteria included significant airflow obstruction or the presence of any medical condition contraindicating challenge testing. Carbachol challenge was performed to assess airway reactivity according to a standardized method. Baseline measurements of forced expiratory volume in 1 s (FEV1), specific airway conductance (SGaw) and the provocative dose of carbachol causing a 35% reduction in SGaw (PD35), and a 20% reduction in FEV1 (PD20) were established on entry while each subject was still smoking. Thereafter, repeat measurements were performed after 2 and 6 months of smoking cessation. Adherence to smoking cessation was checked by self-report and verified by measurement of alveolar carbon monoxide levels at each session. Of the 34 subjects who gave consent, 13 relapsed prior to the 2nd month and an additional 8 relapsed before the 6th month. Thirteen of the 34 remained abstinent throughout the 6-month study. All 13 subjects had complete resolution of their cough. The difference in reactivity on entry to that at the 2nd and 6th month was not significant. We conclude that (1) the symptom of chronic cough resolved completely after 2 months of smoking cessation, and (2) airway reactivity remained unchanged at 2 and 6 months of smoking cessation.