The objective of our study was to investigate the association between daily pediatric asthma hospital visits and daily concentrations of aeroallergens and their specific species. Records of daily asthma visits in Cincinnati area were retrieved from Cincinnati Children's Hospital Medical Center and aeroallergen sampling was performed by the Button Inhalable Sampler. The Poisson generalized linear model was carried out in which the log of the number of asthma hospital visits was related to aeroallergen level, treated as a continuous variable with adjustment for seasonal time trend, day of the week, ozone and PM(2.5) concentrations, temperature and humidity. The aeroallergens having a significant impact on asthma hospital visits were ragweed, oak/maple and Pinaceae pollen. Their relative risks on asthma hospital visits with respect to a 100 counts/m(3) increase in concentration were in the range of 1.23 to 1.54. The effects in causing the asthma exacerbation were delayed by 3 or 5 days.