Whereas evidence of adverse effects of air pollution on lower respiratory tract illnesses in children is increasing, little is known about the effects of high and moderate levels of air pollution on the incidence of upper respiratory illnesses. 9 to 11 year old schoolchildren (n = 1,854) living in Leipzig, East Germany were studied. The presence of upper respiratory symptoms was documented by a physician. Daily mean and maximum concentrations of SO2, particulate matter (PM) and NOx, as well as temperature and humidity, were measured. Furthermore, a self-administered questionnaire was distributed to the parents to assess confounding factors. Parents of 1,500 (81%) children returned the questionnaire. When controlling for paternal education, passive smoke exposure, number of siblings, temperature and humidity, increased risks for the development of upper respiratory symptoms were found in the winter months for SO2 mean concentrations (odds ratio (OR) = 1.72; 95% confidence interval (95% CI) 1.19-2.49). NOx mean concentrations (OR = 1.53; 95% CI 1.01-2.31) and PM maximum values (OR = 1.62; 95% CI 1.08-2.45). In the summer months, only NOx mean concentrations were associated with a significantly increased risk (OR = 1.82; 95% CI 1.21-2.73). A combination of high mean levels of different pollutants resulted in the highest risk (OR = 2.10; 95% CI 1.30-3.37 in the winter, and OR = 2.16; 95% CI 1.23-3.81 in the summer). We conclude that high concentrations of SO2, and moderate levels of particulate matters and NOx are associated with an increased risk of developing upper respiratory symptoms in childhood.(ABSTRACT TRUNCATED AT 250 WORDS)