The prevalence of positive specific IgE antibodies to house dust mites (Dermatophagoides pteronyssinus; D. farinae) was determined by enzyme-linked immunosorbent assay (ELISA) in 5097 (61%) volunteers of 8345 schoolchildren aged between 7 and 14 yr from two government schools. All of them filled out a questionnaire concerning allergic symptoms. Among them, 412 (8.1%) children showed a positive reaction to at least one of the two mite allergens, the range varying between 5.6 and 11.2% according to the child's age. Boys had higher prevalence of positive mite specific IgE than girls (9.8% vs. 6.4%, P less than 0.01), with the overall male to female ratio 1.5:1. The prevalence of bronchial asthma in boys and girls was 5.3% and 3.3% respectively. The positive mite specific IgE antibody in children with asthma and allergic rhinitis was 52% (103 of 198) and 28.7% (193 of 673) respectively. The mean levels of mite specific IgE were not significantly related to the age of onset and severity of asthmatic symptoms (P greater than 0.1), but were significantly different among subjects with current and past asthma (P less than 0.001). It is suggested that the mite-specific IgE may play a role in the pathogenesis of bronchial asthma in children.