BACKGROUND Santiago is a city with a high degree of environmental pollution caused by particulate matter and ozone, producing adverse effects in the respiratory system. OBJECTIVE To compare respiratory symptoms and cough reflex in adults from Santiago and from a rural area with low levels of environmental pollution. METHODS One hundred twenty six non-smoker adults from Santiago and 116 from a rural area with low levels of pollution answered a respiratory symptom questionnaire. Of these 101 subjects from Santiago and 116 from the rural area inhaled doubling concentrations of capsaicin from 0.5 to 500 microM or until five coughs were elicited. The lowest concentration eliciting 2 or more coughs (CD2) or 5 or more coughs (CD5) was recorded. Levels of environmental particulate matter were also recorded in both locations. RESULTS Levels of particulate matter were 102 +/- 41 and 64 +/- 24 micrograms/m3 in Santiago and the rural area respectively. People from Santiago had higher rates of throat clearing, cough and phlegm. CD2 geometric mean and confidence limits in Santiago and the rural area were 6.9 (5.2-7.4) and 2.8 (2.7-2.9) respectively (p < 0.001). No differences in CD5 were observed between both locations. Multivariate analysis disclosed the variable location (city) as the only independent predictor of respiratory symptoms. CONCLUSIONS The increased CD2 found in Santiago suggests that the higher rates of respiratory symptoms related to air pollution can be associated to a decreased sensitivity of the cough reflex.