The standard treatment of allergic rhinitis and asthma consists of topical corticosteroids administered intranasally and inhaled through the mouth. Although this therapy is highly effective, and side-effects are few and mild, it may be possible further to improve the therapeutic index and patient compliance with the treatment. In the present study, we evaluated a nasal inhalation system used for the simultaneous treatment of rhinitis and asthma. In principle, it results in an airway deposition of the corticosteroid similar to that of inhaled allergens. Twenty-four children with perennial rhinitis and asthma inhaled budesonide through the nose from a pressurized aerosol, attached to a spacer device, in a double-blind, placebo-controlled, crossover study. Compared with placebo, budesonide treatment resulted in a significant reduction of nasal symptoms (P<0.01) and of asthma symptoms (P<0.05), and in an increase of nasal peak inspiratory flow (P<0.001) and of oral peak expiratory flow (P=0.01). There were no differences between budesonide and placebo in local side-effects, such as dry nose, nosebleed, and hoarseness. We conclude that nasal inhalation of a corticosteroid from a spacer offers a simple and effective treatment for both rhinitis and asthma in children, but it is an open question whether the nasal inhalation system can improve the ratio of antirhinitis/antiasthma effects to side-effects.