It was the aim of this investigation to study the efficacy of a corticosteroid given as a depot injection in seasonal allergic rhinitis, the efficacy profile with regard to specific symptoms, and whether the injection is best given early in the season or later at the peak of the pollen count. An injection of 80 mg methylprednisolone showed a marked effect on nasal blockage lasting more than 4 weeks, and a moderate effect on eye symptoms, while the effect on nasal hypersecretion and sneezing could not be demonstrated. It is concluded that systemic corticosteroids may be indicated in severe hay fever, when symptoms, especially blockage, occur in spite of other types of therapy. If the physician prefers to give the corticosteroid as a depot injection, it is preferably given in the first half of the season when the pollen count is increasing.