During the ragweed season of 1984 we studied 120 patients with hay fever; 58 had a history of asthma during the ragweed season the year before. They were divided into four treatment groups to receive nasal sprays of placebo, cromolyn sodium, flunisolide, or beclomethasone. In controlling hay fever symptoms all medications were superior to placebo; the glucocorticoids were more effective than was cromolyn sodium. Chest symptoms in the 58 patients with a history of asthma were also relieved by the topical nasal treatment. Various explanations for the beneficial effect of topical nasal treatment in asthma symptoms are conceivable. We consider the most likely to be improvement of nasal airway function. With restoration of the filtering action of the nose, less allergen would penetrate to the intrathoracic airways because of reduction in mouth breathing.