In this thesis, acute respiratory health effects of exposure to winter air pollution are investigated in panels of children (7-11 yr) and adults (50-70 yr) with and without chronic respiratory symptoms, living in urban and non-urban areas in the Netherlands. The study was performed during three consecutive winters starting in 1992/1993. Each winter, subjects performed twice daily measurements of Peak Expiratory Flow (PEF) and registered the occurrence of respiratory symptoms and medication use in a diary. Air pollution concentrations were measured daily in both areas.The contrast in the concentrations of particulate air pollutants (PM 10 , Black Smoke and sulfate) between urban andnon-urban areas was small, but there was more contrast in the concentrations of the gaseous pollutants SO 2 and NO 2 .In symptomatic children from both areas, significant associations were observed between PM 10 , Black Smoke (BS) and sulfate concentrations and the prevalence of lower respiratory symptoms (LRS) and PEF decrements. Particle concentrations were also associated with bronchodilator use in the urban areas, but not in the non-urban areas. However, differences in use of maintenace medication might be responsible for this. In non-symptomatic children, significant associations were observed between PM 10 and BS concentration and the prevalence of PEF decrements, but of smaller magnitude than for symptomatic children. No associations with respiratory symptoms were observed.In symptomatic adults living in urban areas, PM 10 , BS, sulfate and SO 2 concentrations were associated with the prevalence of decrements in morning PEF, but not in evening PEF. Although especially BS was also associated with upper respiratory symptoms, particle concentrations were not associated with LRS or bronchodilator use. In symptomatic subjects living in non-urban areas, and in non-symptomatic adults from both urban and non-urban areas, no consistent associations between air pollution concentrations and indicators of respiratory health iwere ...