It is reasonable to suppose that airway mucosa can be damaged by irradiation applied to chest and neck regions. The inflammatory process is a consequence of an injury. Airway inflammation is one mechanism responsible for cough induction. So, one can suppose that radiotherapy (RT) focused on the patients' chest or neck may injure airway mucosa, which might change sensitivity of the nerve-endings mediating the cough reflex. The purpose of this study was to examine cough reflex sensitivity (CRS) in patients who underwent RT in the chest and neck regions. CRS test using capsaicin was performed in patients with breast cancer (Group A, n=19), and with lung or neck cancer in (Group B, n=14) who underwent RT. Capsaicin aerosol in doubled concentrations (0.49-1000 microM) was inhaled by a single breath. CRS was defined as the lowest capsaicin concentration that evoked 2 or more coughs (C2). Radiation doses ranged from 40 to 70 Gy. Capsaicin cough challenge was performed before and then in the 2(nd) and 5(th) week of RT. We observed a significantly reduced value of C2, i.e., increased cough reflex sensitivity, in Group B in the 2(nd) week of RT (P= 0.04). We conclude that CRS in the lung or neck cancer patients undergoing RT is significantly enhanced, which could result from injury to the nerve endings in airway mucosa.