A double-blind parallel trial of budesonide versus placebo was carried out in 19 patients suffering from nasal polyposis. The patients were randomly assigned to two groups, one receiving a daily dose of 400 micrograms of budesonide and the other a corresponding dose of placebo intranasally for 4 months. The total mean symptom scores and nasal peak flow values during the trial showed a statistically significant difference in favour of budesonide. On rhinoscopy, a clear decrease in mucosal congestion was noticed in the group receiving the active drug. The polyps diminished in number and size in the budesonide group. Mucociliary function, measured by the saccharin test before and after therapy, did not undergo significant changes in either group. Mean plasma cortisol values were of the same order before and after therapy. Local side-effects were mild in both groups, and there was no indication of mucosal drying or crusting attributable to the test solution. Pre- and post-therapy biopsies revealed a pronounced decrease in tissue eosinophilia following budesonide treatment. Neither nasal smears nor biopsies showed signs of morphological changes in the epithelium.