We assessed the relationship between the exposure to dust mite allergens and a bronchial response to exercise in 8-year-old schoolchildren. Dust was collected from the mattresses of 1,291 children and the concentration of mite allergens was estimated by a commercially available ELISA test using monoclonal antibodies (ALK, Copenhagen) against the major allergens of Dermatophagoides pteronyssinus (Der pt) and Dermatophagoides farinae (Der f). A positive bronchial response to exercise (decrease of peak expiratory flow > or = 15% after exercise) occurred in 21 (22.6%) of 101 children sensitized to mite allergens (wheal size > or = 4 mm) and in 51 (4.8%) of 1,070 nonsensitized children. In the highest exposure groups (> 10 micrograms allergen/g dust), 15% of children sensitized to Der f and 20% of children sensitized to Der pt were responsive to exercise. Corresponding figures for the lowest exposure groups (< 0.4 micrograms allergen/g dust) were 11 and 28%, respectively. This negative finding may indicate that measurement of allergen concentration in mattresses does not reflect true exposure or alternatively that at the age of 8 years high exposure to dust mite allergens does not affect bronchial response to exercise in sensitized children.