A methacholine challenge or bronchial challenge test is a test for asthma and other bronchial diseases. The patient is given methacholine or histamines to inhale in a fine powdered form. The drugs encourage the bronchial passages to constrict. The patient is then put through a series of tests of their lung capacity. Eventually, the patient will have a reduction in lung capacity, but in asthmatic patients this will happen at lower doses of the drugs.