In a double-blind group comparative study, 36 adult, birch pollen-allergic outpatients with seasonal rhinoconjunctivitis, were treated with either oral prednisolone 7.5 mg daily for 3 weeks or an injection with 2 ml suspension of betamethasone dipropionate and betamethasone disodium phosphate (Diprospan®) immediately prior to the birch pollen season. Both treatments were able to prevent an increase in symptoms from the nose and the eyes during the 3-week birch pollen season. There was no significant difference in symptom score or nasal peak flow between the two treatments. However, there was a significant suppression of adrenal gland function after oral prednisolone treatment in contrast to Diprospan treatment. Unless there are contraindications for treatment with depot steroid injections (children, pregnant women, patients suffering from peptic ulcer, tuberculosis, eye disease, herpes, hypertension or diabetes) it seems to be a reasonable alternative to ored prednisolone in hay fever patients.