The aim of this study was to describe the impact of using bronchodilators on the prevalence of Chronic Obstructive Pulmonary Disease in a population-based survey (Platino study). A cluster sampling of subjects 40 years of age or older, representative of the metropolitan areas of 5 Latin American cities (Sao Paulo, Mexico, Montevideo, Santiago and Caracas) was chosen. Spirometry according to ATS standards was done before and after inhalation of 200 micrograms of salbutamol in 5183 subjects. Prevalences of airflow obstruction were estimated using different criteria, in tests done before and after bronchodilator use, and with reference values for pre- or post-bronchodilator use. Bronchodilator testing reduced the overall prevalence of FEV(1)/FVC% < 0.70 from 21.7% to 14% (35%). In the group with FEV(1)/FVC < 0.70 after bronchodilator use, 21% were asymptomatic from the respiratory point of view, and lacked significant adverse exposures. Subjects below the 5th percentile for FEV(1)/FVC and FEV(1)/FEV(6) were fewer than those with FEV(1)/FVC < 0.70, especially among the elderly. More subjects are below the 5th percentile of FEV(1)/FVC and FEV(1)/FEV(6) using reference values for tests after bronchodilator use than using the reference values determined without bronchodilator testing. Testing after bronchodilator use reduces the prevalence of airflow obstruction from 32 to 39% depending on the definition used. In addition, the subjects who were still obstructed after bronchodilator use were the ones who showed more respiratory symptoms and exposure to tobacco and other smokes and dusts, than subjects with reversible obstruction, suggesting an increased specificity for COPD.