Clinical studies were performed to evaluate the role of the vidian nerve at onset of symptoms in nasal allergy. A localized area of one side of the nasal cavity was stimulated with known allergen and 0.1% histamine chloride in patients with perennial nasal allergy. The effect of unilateral vidian neurectomy and sensory anesthesia on glandular and vascular response was evaluated. With localized nasal stimulation, hyperrhinorrhea was seen in both sides of the nasal cavity before vidian neurectomy. Unilateral vidian neurectomy blocked hyperrhinorrhea only in that nasal cavity in which the nerve was sectioned. However, hyperrhinorrhea from the contralateral side, with an intact vidian nerve, was blocked with sensory anesthesia of the opposite side of the nasal cavity where the stimulation was applied. Nasal hypersecretion in allergic rhinitis was assumed to be mostly due to stimulation of sensory receptors by a chemical mediator and reflexive stimulation of the nasal glands. Vidian neurectomy, however, did not have any apparent influence on the swelling of the nasal mucosa caused by localized stimulation of allergen and histamine.