This article is a commentary on a study published in the journal Am J Respir Crit Care Med. 2002;166:1092-8. It is a cohort study of Dutch newborns that examines the role of long-term exposure to road traffic in the development of respiratory symptoms between 12 and 24 months of age. Air emissions from road traffic constitute one of the major sources of air pollution, accounting for a wide range of pollution indicators such as nitrogen oxides, particulate matter, benzene, and carbon monoxide. Although numerous epidemiological studies have demonstrated the link between exposure to air pollution and respiratory health, few have examined the specific role played by traffic. The originality of this prospective study lies in the individual estimation of exposure to pollutants. It combines data from a measurement campaign with traffic parameters using a geographic information system (GIS). This is a methodologically sound study, innovative in terms of exposure assessment, which highlights a relationship between exposure to traffic-related pollutants and respiratory symptoms (particularly wheezing and a diagnosis of asthma) under specific conditions (urban setting and less than 10 hours per week in daycare). These results will need to be verified during follow-up, when asthma diagnoses can be confirmed. A more detailed analysis accounting for different asthma phenotypes could complement these findings. (Excerpts from the article)