The impact of summertime haze episodes on daily variations in symptoms and peak expiratory flow rates (PEFRs) was examined in a study of 108 children living in State College, Pennsylvania, during the summer of 1991. Twice daily, each child recorded symptoms, PEFRs and hours spent outdoors. Environmental measurements included daily 12- and 24-hour averages for meteorologic and air pollutant variables and 24-hour average fungus spore concentrations. A 10,000-spore/m3 increment in Cladosporium spore concentration was associated with a deficit in morning PEFR (-1.0 liters/minute, 95% confidence interval (CI) -1.9 to -0.2). A 60-spore/m3 increment in Epicoccum spore concentration was associated with increased incidence of morning cough (odds ratio (OR) = 1.8, 95% CI 1.0-3.2) and a deficit in morning PEFR (-1.5 liters/minute, 95% CI -2.8 to -0.2). Fungi spore counts were not associated with respirable particle mass. A 125-nmol/m3 increment in 12-hour daytime particle-strong acidity was associated with a deficit in evening PEFR (-0.5 liters/minute, 95% CI -1.2 to 0.2) and increased incidence of cold episodes that evening or the subsequent morning (OR = 1.35, 95% CI 1.14-1.61). A 20-microgram/m3 increment in 24-hour respirable particles lagged by 24 hours was associated with a deficit in evening PEFR (-0.5 liters/minute 95% CI -1.4 to 0.4) and increased incidence of cough episodes that evening or the subsequent morning (OR = 1.37, 95% CI 1.13-1.66). These results confirm the acute effects of summertime particulate air pollution and suggest that aeroallergens have independent effects on respiratory symptoms and PEFR in children.