The purpose of this work was to examine in a double blind study the ability of beclomethasone dipropionate to prevent recurrence of nasal polyps in patients in whom radical ethmoidectomy had been performed immediately before. It analyzes the results in terms of the patients subjective symptoms, clinical status and rhinomanometry. After the follow-up period of one year 86% of the patients in the beclomethasone group and 60% in the placebo group had no subjective nasal symptoms. In clinical examination polyps were absent in 54% in the beclomethasone group and in 13% in the placebo group. Rhinomanometrically there was normal nasal patency in 68% in the beclomethasone and in 33% in the placebo group.