A double-blind, double-dummy comparative study was made of 30 adult birch pollen-allergic outpatients with seasonal rhinoconjunctivitis. They were treated with either topically applied beclomethasone dipropionate 100 μg in each nostril twice daily for 4 weeks, placebo, or an injection of 2 ml of a suspension containing 5 mg bethamethasone dipropionate and 2 mg betamethasone disodium phosphate per ml (Diprospan®) immediately prior to the birch pollen season. Placebo- and topical steroid-treated patients experienced an increase in rhinoconjunctivitis symptoms, i.e. nasal blockage, nasal itching, rhinorrhea, sneezing and eye symptoms, and placebo-treated patients used significantly more antihistamine tablets during the pollen season. Diprospantreated patients experienced fewer symptoms on all measured parameters. We concluded that one injection of Diprospan immediately prior to the birch pollen season produces significantly fewer rhinoconjunctivitis symptoms than does placebo and topical steroid treatment.