The purpose of this review is to present data on nasal reactivity to methacholine, histamine and allergen in normal subjects, patients with common colds, perennial rhinitis and hay-fever. Nasal challenge is performed by spraying the agent into the nose and counting the sneezes, measuring the resulting secretion and the increase in nasal airway resistance during a 15 minute period. We found that there was a small increase in reactivity during a common cold, but a considerable increase during the hay-fever season and associated with perennial rhinitis. We conclude that a nasal challenge test may be a valuable tool as an objective parameter for the diagnosis and for the estimation of the severity of rhinitis. It may also be helpful in the evaluation of new drugs and give information regarding pathogenetic mechanisms as well as the mode of action of specific drugs.