During the winter of 1994, the association between daily changes in air pollution and in the respiratory health of children 7 to 12 yr of age were studied in Kuopio, Finland. Seventy-four children with asthmatic symptoms and 95 children with cough only, living either in urban or suburban areas, were followed for 3 mo. During the study period, the mean daily concentration of particulate air pollution (PM10) was 18 micrograms/m3 in the urban area and 13 micrograms/m3 in the suburban area. Lagged concentrations of PM10, black smoke, and NO2 were significantly associated with declines in morning peak expiratory flow (PEF) among asthmatic children. The regression coefficient (x10) for a 2-d lag of PM10 was -0.911 (SE, 0.386) in the urban and -1.05 (0.596), in the suburban area. Among children with cough only, PM10, black smoke, and NO2 were not significantly associated with PEF. In the urban area, there was a significant association between SO2 and morning and evening PEF and incidence of upper respiratory symptoms among children who cough only. No other associations between air pollution and evening PEF or respiratory symptoms were observed. This study suggests that particulate air pollution is associated with respiratory health, especially among children with asthmatic symptoms.