Intranasal budesonide, 400 micrograms two times a day, was evaluated in 36 patients referred for treatment of nasal polyposis. The age range was 20 to 68 years. Polypectomy was done 5.6 (mean) times previously. After a 5-week, treatment-free, baseline period, patients were treated in a double-blind fashion with either budesonide or placebo during 4 weeks. After this treatment period, placebo-treated patients started receiving budesonide in an open trial for an additional 4 weeks. The patients rated their nasal symptoms daily. Nasal examinations and nasal inspiratory flow rate (IFR) measurements were done at clinic visits. After 3 and 4 weeks of treatment, the response to budesonide was significantly greater than response to placebo. The greater reduction in nasal blockage caused by polyps, observed on physical examination, p = 0.005, was mirrored by an increase in nasal IFR (p = 0.0001). Patient rating of the severity and frequency of nasal blockage were reduced more by budesonide than by placebo (p less than or equal to 0.0005). Switching placebo-treated patients to budesonide treatment resulted in a reduction of nasal blockage (p less than 0.001) and an increase in nasal IFR (p less than 0.001). The results demonstrate that topical nasal budesonide, 400 micrograms two times a day, is an effective treatment of nasal polyps.