Twenty-five patients with massive nasal polyposis were treated during four days with 60 mg oral prednisolone (Deltacortril) followed by a progressive reduction of the dose (minus 5 mg per day). Therapeutic efficacy was evaluated by means of symptoms, anterior rhinoscopy, and a CT scan of the sinuses before and at the first visit after the treatment. Seventy-two per cent of the patients showed subjective improvement due to the involution of polyps in the nasal cavity. However, on CT of the paranasal sinuses only 52% showed a clear improvement. In general, the frontal and sphenoid sinuses were more likely to clear up completely than were the ethmoidal and maxillary sinuses. Therapeutic efficacy seemed to be better in the group of ASA-intolerant patients and worse in the allergic group. The "intrinsic" group showed an equal distribution of good results. Also, the presence of eosinophils in polyps played no role in the therapeutic outcome. We found a strong tendency of recurrence within five months after successful oral steroid therapy. On the other hand, pre-operative systemic steroid therapy considerably facilitated the surgical procedure. Keeping in mind the side effects of systemic steroid therapy, this treatment should be mainly reserved for cases in which surgery is planned.