Inhaled furosemide decreases bronchial response to several physical and chemical irritants. To evaluate the effect of topical furosemide on nasal resistance in patients affected by perennial nonallergic rhinitis, we studied 12 patients. This diagnosis of perennial nonallergic rhinitis was based on the history of rhinorrhea, sneezing, and nasal obstruction, on anterior rhinoscopy and endoscopy, on negative allergic tests, and on the absence of eosinophilia in nasal secretion. The study was performed on two nonconsecutive days. On the first day, one puff (100 microliters) of 0.9% saline was sprayed into both nostrils and nasal resistance was measured by anterior rhinomanometry before the puff and 15 and 30 minutes later. On the second day, one puff (100 microliters) of a solution of furosemide (10 mg/mL) was sprayed into both nostrils and nasal resistance was measured before the puff and 15, 30, 45, 60, 90, 120, and 180 minutes later. Initial nasal resistance was abnormally high in all patients on both days. A slight but significant increase was observed after spraying isotonic saline (base: 1.38 +/- .69; 15 minutes: 1.47 +/- 0.72; 30 minutes: 1.44 +/- 0.73); by contrast a marked decrease was observed after spraying the furosemide solution. Nasal resistance was lowest between 30 and 90 minutes after giving furosemide. Then it progressively increased, but values at 180 minutes were still lower than the initial ones (base: 1.43 +/- 0.67; 15 minutes: 0.70 +/- 0.47; 30 minutes: 0.48 +/- 0.24; 45 minutes: 0.49 +/- 0.21; 60 minutes: 0.50 +/- 0.20; 90 minutes: 0.56 +/- 0.23; 120 minutes: 0.62 +/- 0.32; 180 minutes: 0.67 +/- 0.30). After topical furosemide, all patients had subjective relief of nasal obstruction that lasted more that 12 hours in 9 subjects.