To compare the antiasthmatic efficacy of inflammatory mediator blockade versus topical corticosteroid therapy in patients with seasonal allergic rhinitis (SAR) and asthma, 14 patients were enrolled into a single-blind, double-dummy, placebo-controlled crossover study comparing 2 wk therapy of ( 1 ) 400 g orally inhaled budesonide plus 200 g intranasal budesonide (BUD) or ( 2 ) 10 mg oral montelukast plus 10 mg oral cetirizine (ML ϩ CZ). Before each treatment period, patients received 7 to 10 d placebo washout. All treatments were given once daily in the morning. Throughout the study, patients recorded the following domiciliary measures: peak expiratory flow (PEF), rescue inhaler requirement, asthma symptoms, and daily activity score. Laboratory measurements were made at trough of adenosine monophosphate (AMP) bronchial challenge and exhaled nitric oxide (NO). Compared with pooled placebo (PL), there were significant (p Ͻ 0.05) improvements in all domiciliary measures with both treatments (mean PEF [L/min] PL: 463; BUD: 478; ML ϩ CZ: 483). For geometric mean AMP PC 20 (mg/ml), there was an improvement (p Ͻ 0.05), compared with PL (47), for ML ϩ CZ (133) but not for BUD (51); whereas for NO (ppb) there was significant suppression with BUD (7.6) but not ML ϩ CZ (11.5) compared with PL (13.6). In conclusion, both combined mediator blockade and combined topical corticosteroids are equally effective antiasthma therapy in patients with asthma and SAR.Asthma and allergic rhinitis are common conditions, occurring with increasing prevalence, and frequently coexisting (1). Both conditions occur in patients with underlying atopy and have a common etiology and pathophysiology. Untreated rhinitis can result in increased lower respiratory tract inflammation (2) due to a variety of possible mechanisms (3). There is good evidence to show that treating the upper airway inflammation in seasonal allergic rhinitis with intranasal corticosteroids alone has beneficial effect on lower airway inflammation in terms of an improvement in bronchial hyperreactivity (4).Topically delivered inhaled and intranasal corticosteroids are widely recognized as effective anti-inflammatory treatment for both conditions (5, 6). They work by altering gene transcription to increase or decrease a plethora of cytokines, inflammatory mediators and enzymes, and adhesion molecules (7). Histamine and cysteinyl leukotrienes are important inflammatory mediators in the pathogenesis of asthma and allergic rhinitis. With the introduction of leukotriene receptor antagonists it is now possible to selectively block the effects of both of these mediators. This may have a theoretical advantage over corticosteroid therapy as a result of a better adverse effect profile as well as the preference for taking tablets rather than inhalers and nasal sprays.The anti-inflammatory properties of leukotriene receptor antagonists have been shown to exhibit beneficial effects on asthma disease control (8). Antihistamines have been considered to be effective in the management of asthma ...