Allergen provocation in the nose increases the non-specific nasal reactivity. The aim of this trial was to determine whether this 'priming effect' can be caused by histamine or methacholine, which is the most important biochemical mediator of allergic rhinitis, and an analogue to the important neurotransmittor, acetylcholine, respectively. Intranasal provocation tests with the two substances were carried out on thirteen normal subjects, and repeated 1 hr and 1 day later. The response, measured as the number of sneezes, the amount of blown secretion and the increase in nasal airway resistance, did not change with consecutive provocations. It was concluded that neither histamine nor methacholine were responsible for the allergen-induced 'priming' of the nasal mucous membrane.