The effect of topical anaesthesia on the nasal mucosa before and after allergen challenge was evaluated in 12 subjects with strictly seasonal allergic rhinitis. A single-blind randomized placebo-controlled design was used. The nasal challenge was carried out after pre-treatment of the nasal cavity with 52 mg of lidocaine/nasal cavity, or placebo applied topically in spray form. The number of sneezes was counted. The amount of nasal secretion was estimated by weighing used paper handkerchiefs. The capacitance and resistance vessel reactions were monitored by determining nasal peak flow and 133Xe wash-out respectively. After placebo pre-treatment the two doses of allergen induced moderate symptoms and vascular changes. Pre-treatment with local anaesthesia did not affect any of the symptoms nor did it affect the decrease in the tone of the capacitance vessels. It was found that topically applied lidocaine per se did not have any effect on nasal mucosal blood flow as measured using the 133Xe wash-out technique. However, the local anaesthesia did block the allergen-induced increase in the tone of the resistance vessels. In conclusion, a redundancy of systems appears to be involved in nasal allergic reactions. Although a reflex-induced mechanism may well play a significant role in the induction of the signs and symptoms of nasal allergic reactions, the redundancy of systems involved may well override any reduction in one single system, as appears to be the case in the present study. Lidocaine peer se did not influence the nasal mucosal blood flow.