Ten years' experience of standardised bronchial histamine and methacholine tests is presented. For measuring non-specific hyperreactivity was used an internationally adopted dose-response technique, where histamine or methacholine is inhaled at doses increasing in two-fold steps. The fields of application have been clinical research on hyperreactivity, the diagnosis of asthma, evaluation of anti-asthmatic drugs, establishing (or excluding) the presence of bronchial obstruction or functional breathing disorder--the latter being a relatively new field. On the basis of this experience, the existence of a relationship between subjective hyperreactivity and breathing complaints has been hypothesized; and in clinical studies the place of histamine and methacholine tests as diagnostic aids in cases of bronchial asthma or functional breathing disorder has been better established. The tests yield information as to any tendency to develop bronchospasm, but must always be combined with other diagnostic tests and the taking of a careful history. Some important findings are reported--e.g., abnormal and steep dose-response curves, false low FEV1 values, or the occurrence of non-asthmatic symptoms during testing--which have not previously been fully considered in published reports, and which may lead to incorrect interpretation of test results.