Background. The relationship between air pollution and health damage has been sufficiently documented. In station "R" of the air quality monitoring system, located in a community of Metropolitan Santiago (Cerro Navia), the Chilean standard of 150 mu g/m(3), averaged in 24 hours, for particles with a diameter of 10 micrometers or less (PMTO), has been exceeded more days than in the rest of the city stations. Aim: To investigate if the population living near that station has a higher proportion of lower respiratory infections than the Metropolitan Region (MR) as a whole. Material and methods: An outpatient clinic located near station "R" (Centro Albertz), was implemented as a sentinel center according to UNICEF methodology, used since 1992 by the Acute Respiratory Infections National Program. Daily information was collected between May and December 2004. Monitoring data included total number of consults by children less than 15 years old, for lower respiratory tract infections, pneumonia, obstructive bronchitis syndrome in children and by adults over 64 years old for lower airway disease, chronic obstructive pulmonary disease (COPD), carol pneumonia. Results were compared with those of the rest of MR. Results: Compared with the MR, children from the sentinel clinic bad a significantly higher proportion of consults for obstructive bronchial syndrome (20.1916 and 264% respectively, in p < 0.01) and pneumonia (1.3 and 2.7% respectively, p < 0.01). In the elderly, the average consults for lower airway disease were 17% in the sentinel clinic and 12.2% in MR (p < 0.04). Conclusions: Children and elderly subjects at the sentinel clinic had a significantly higher proportion of respiratory infections (pneumonia and obstructive bronchial syndrome in children and lower airway disease in the elderly) as compared to the Metropolitan Region.