The relation between the frequency of wheezing illness and IgE antibody levels against Dermatophagoides farinae (Df) and total IgE levels was examined in 457 randomly selected schoolchildren. From the response to the ATS-DLD-78-C respiratory symptoms questionnaire, 14 subjects (3.1%) were found to have asthma syndrome (recurrent episodes of attacks of shortness of breath with wheezing) and 17 subjects (3.7%), wheezing syndrome (only wheezing). The percentage of the asthma syndrome increased with increasing levels of Df-specific IgE, and there was an intimate correlation between the percentage of asthma syndrome and Df-specific IgE levels (r = 0.97; p less than 0.001), whereas such association was not found between the two (r = -0.19; p greater than 0.5). Similar relations were found between the frequencies of the specific syndromes and total IgE levels. There was a significant correlation between total IgE levels and Df-specific IgE levels in the total population (r = 0.7; p less than 0.001). These results suggest that allergic reaction greatly contributes to the development of asthma in children.