Corticosteroids are effective in controlling the inflammatory component of allergic rhinitis; however, evidence for the clinical efficacy of systemic corticosteroids in this disease is sparse. It is further common practice to combine oral corticosteroids with antihistamines in the treatment of acute exacerbations of allergic rhinitis. The aim of this study was to investigate the effect of low-dose oral betamethasone alone and in combination with loratadine in a group of patients with allergic rhinitis with clinically significant obstruction. In this parallel, double-blind, active controlled multicentre study, 299 patients with severe allergic rhinitis were randomly allocated to either betamethasone 1.0mg or betamethasone 1.0mg plus loratadine 10mg or betamethasone 0.5mg plus loratadine 10mg or loratadine 10mg alone for 5-7 days. Total symptom scores, nasal obstruction, and doctor and patient perception of improvement were measured as markers of disease severity. Although not statistically significant, both betamethasone 1.0mg regimens resulted in a total symptom score difference of at least 1 or more from loratadine (i.e. mean [SD] change in total symptom score of 4.10 [3.10] and 4.40 [3.62] vs 3.10 [3.30], respectively, for betamethasone 1.0 mg plus loratadine, betamethasone 1.0 mg and loratadine). All corticosteroid-containing regimens were significantly better than loratadine alone with regard to the patients' (p < 0.013) and doctors' (p < 0.009) perceptions of improvement. They significantly favoured loratadine in combination with betamethasone over single-drug therapy (i.e. odds ratio: investigator ratings 0.49, 0.36 and 0.45, and patient ratings 0.47, 0.40 and 0.43, respectively, for 0.5 mg and 1.0 mg betamethasone plus loratadine and betamethasone 1.0 mg alone vs loratadine alone). Betamethasone 1.0mg plus loratadine also resulted in significant reduction of the relapse rate compared with the other therapies. This study demonstrated the benefit of a short course of a systemic low dosage of corticosteroids with and without antihistamine therapy during acute severe exacerbations of allergic rhinitis. Combination treatment with betamethasone 1.0mg and loratadine 10mg was significantly better in relieving symptoms of hayfever as experienced by patients. This was the first study to give evidence of benefit of systemic low-dose corticosteroids with and without an antihistamine in patients with acute exacerbations of allergic rhinitis.