In the last decade the prevalence of asthma and allergy is increasing. Epidemiological studies have frequently shown that allergic diseases and asthma are more prevalent in children living in areas with relative high traffic intensity. To study whether the urban air pollution adversely affects the allergic responses to pollen and house dust mite, the present study was performed in allergic and non-allergic children living in the city of Utrecht (Zuilen and Ondiep). 119 Schoolchildren were selected and they were divided into 4 groups: children without allergy, and children allergic for pollen, for house dust mite or for both pollen and house dust mite. Besides the completing a diary, the higher and lower respiratory tract of children were investigated using non-invasive sampling procedures. The results show that the levels of air pollution in the region Zuilen/Ondiep, measured in the study, are normal for urban regions and below the current standards. Between the groups with different ethnic origin differences in prevalence of allergic sensitisation were observed. Children sensitised to pollen, house dust mite or to both allergens, do not show an increased prevalence of complaints during exposure to pollen or increased levels of airpollution. This is objectified by the results obtained in the study measuring biomarkers in exhaled air and nasal lavage. In conclusion, children allergic for airway-allergens (based on positive skin test) have significant more respiratory complaints than children who were negative in this test. However, during this study air pollution did neither facilitate a stronger allergic reaction nor did it result in more respiratory complaints in school children living in the regions Zuilen and Ondiep.