The short-term association of particulate air pollution with peak expiratory flow rate (PEF) and respiratory symptoms was examined. Forty-nine children with chronic respiratory symptoms aged 8-13 yrs were followed daily for six weeks in spring, 1995, in Kuopio, Finland. Daily concentrations of particulate material with a 50% cut-off aerodynamic diameter < or = 10 microm and < or = 2.5 microm (PM10 and PM2.5, respectively), black carbon, and the number concentrations of particles from 0.01-10 microm diameter were measured. During the study period, PM10 were mainly resuspended soil and street dust, and the concentration was estimated using aluminum content of PM10 samples. No consistent effect of particles was found as the associations varied by lag. Of the lags examined, only 1-day lagged PM2.5 was statistically significantly associated with morning PEF (beta=-1.06, SE=0.52 (per interquartile increase in pollutant)). Evening PEF was significantly associated with the 1-day lagged number of particles in the size range 0.1-1.0 microm (beta=-1.56, SE=0.72). One-day lagged PM10, PM2.5-10, PM2.5 and resuspended PM10, and 4-day average of PM2.5 were significantly associated with increased risk of cough. Given the short duration of the study, separating the effects of different types of particles was difficult. The present study demonstrates the highly variable size and number distribution and chemical composition of particles in Finland, and underlines the importance of measuring the size and chemical composition of particles to determine which types of particles are associated with health effects.