To study the prevalence and possible predictors of bronchial responsiveness we examined a cross-section of 527 children aged 7-16 years from Copenhagen. The method used included an interview with the child and the parents, skin prick test with common allergens and se-IgE. Bronchial responsiveness was measured by a histamine inhalation test. We found that 79 (16%) of the children had bronchial hyperresponsiveness (BH), defined as a 20% fall in FEV1 with a provoking concentration of histamine (PC20) at 8 mg/ml or less. Atopic symptoms defined as asthma, rhinitis or eczema were significantly (P less than 0.001) correlated to BH both in prevalence and degree of BH. None of the children with urticaria had BH. The degree of bronchial responsiveness was also significantly influenced (P less than 0.001) by family disposition to atopy, whereas we found no correlation between BH and "passive" smoking, specific skin test in unselected children, or elevation of IgE in children without atopic symptoms. We conclude that BH is severest in children with asthma, independent of elevated IgE or positive skin prick test. Children with rhinitis, dermatitis, or asymptomatic BH have the same degree of BH; this differed from that in children with asthma.