In order to explore the relationship between bronchial hyperresponsiveness (BHR) to inhaled histamine, respiratory symptoms and diagnosed asthma in children, we undertook a cross-sectional study of 2363 Australian schoolchildren aged 8-11 years. The methods used included a self-administered questionnaire to parents, which was shown to have a high degree of repeatability, and a histamine inhalation test to measure bronchial responsiveness (BR). The study showed that 17.9% of children had BHR, defined as a 20% fall in FEV1 at a provoking dose of histamine (PD20 FEV1) of less than 7.8 mumol. The distribution of PD20 FEV1 appeared to be continuous. Most children with PD20 FEV1 values less than 1.0 mumol had symptoms of asthma. However, 6.7% of children had BHR without symptoms or a previous diagnosis of asthma and 5.6% had had a diagnosis of asthma but had no BHR. Although there was a good association between BHR and respiratory symptoms, questionnaire data of wheeze and diagnosed asthma do not reflect accurately the level of BHR in the community. We conclude that cross-sectional studies of BR to identify children with BHR probably do not reflect the prevalence of asthma in populations of children. However, the strong association between BHR and symptoms, particularly in children with severe and moderate BHR, suggests that measurements of BR in populations are useful for defining a group of children whose airways behave differently from those of the majority. Prospective studies are needed to define the level of BHR that is associated with important sequelae.