Sildenafil (Viagra; Pfizer), a phosphodiesterase inhibitor, promotes penile erection through increased intracellular cyclic guanine monophosphate (a second messenger) in response to nitric oxide (a first messenger) release following sexual stimulation. Nitric oxide is involved in nasal vasodilation, secretion, and mucociliary clearance. The aim of this study was to assess the effect of sildenafil on nasal patency.Pilot study.Teaching hospital.Nasal patency was assessed by a visual analogue score and by measurement of the peak nasal inspiratory flow (PNIF) in five subjects before and after administration of sildenafil.Visual analogue score and PNIF.There was a significant increase in the subjective sensation of nasal obstruction (p = .003; -9.6 +/- 2.7, -15.4 to -3.7 [mean +/- SEM, 95% CI) and a significant reduction of PNIF (p < .001; 70.7 +/- 13.2, 43.1 to 98.3).This pilot study suggests that nasal patency may be reduced following the administration of sildenafil. The role of phosphodiesterase inhibitors in nasal physiology merits further investigation.