Sildenafil shows an intense and prolonged inhibitory effect on the smooth muscle cells of corpus cavernosum arterioles by blocking phosphodiesterase type 5 that inactivates the nitric oxide-stimulated cyclic guanosine monophosphate. We investigated if this inhibitory effect is also displayed on smooth muscle cells of the esophagus. In 16 normal subjects (9 men and 7 women, mean age 34 years, range 22-56) esophageal motility was recorded by means of a low-compliance manometric system with side holes for the esophageal body and a sleeve for the lower esophageal sphincter (LES). After a basal period of 60 min, a tablet of sildenafil 50-mg ground and dissolved in water was infused in the stomach in eight subjects (group A) and a placebo tablet in the other eight subjects (group B), randomly and in a double-blind manner; the recording continued for another 60 min. LES tone and postdeglutitive residual pressure, as well as amplitude, propagation velocity, and onset latency of contractions were measured each minute, the values averaged every 5 min, and the mean of the entire basal and postinfusion periods was calculated. The postinfusion values were compared with the basal values in each group and with the corresponding values of the other groups. The percent variations of postinfusion values with respect to basal values were also compared. Sildenafil induced a statistically significant decrease of LES tone, residual pressure, wave amplitude, and propagation velocity and a significant increase of onset latency of pressure waves in comparison with the values of the basal period and placebo. The inhibitory effect reached its maximum 10-15 min after the infusion and lasted about 1 hr. In conclusion, sildenafil markedly inhibits the motor activity of the esophageal musculature by decreasing LES pressure, wave amplitude, and propagation velocity and increasing the onset latency of pressure waves.