A type of chemical used in challenge testing. Everybody's airways respond to it, but the airways of a person with asthma respond much more and at lower doses.

A substance used to test for increased airway responsiveness (or reactivity) in bronchial provocation tests during which increased doses of methacholine are inhaled to determine if the airways are more sensitive than normal, such as in asthma patient (see bronchial hyperactivity).

parasympathomimetic drug (trademark Mecholyl) that stimulates secretions and smooth muscle activity