Elevated levels of particulate matter can exacerbate existing asthma and atopy, while evidence that it can promote the induction of atopy and asthma is limited. A cross sectional study was taken to compare the prevalence of eye, nose, ear and airway allergic symptoms, allergic skin sensitivity and lung function in 290 high school students with a history of high 24 hour average exposure to particulate matter less than 10 microm in diameter (PM10) = 170 microg/m3 versus low PM10 of 36 microg/m3 in central Bangkok. Multivariate analysis revealed an increased risk of eye and airway symptoms in groups exposed to higher PM10 levels (p = 0.003, and 0.05, respectively). Positive skin prick tests and a history of having a lawn at home were associated with nasal symptoms (p = 0.008 and 0.04, respectively). Mean FEF(25-75%) (forced expiratory flow that occurs during the middle 50% of the forced expiratory effort) was significantly lower in those who were exposed to higher PM10 levels (3.89 +/- 1 vs 4.42 +/- 0.9 l/sec, p < 0.001). A significant increase in days of school absence and medical expenses was associated with high PM10 exposure. It is concluded that chronic exposure to high PM 10 levels was significantly associated with increased prevalence of eye and airway symptoms and a decrement of FEF(25-75%) resulting in increase of school absence and medical expense.