Objective: As recently suggested, nitric oxide (NO) may play an important role in the regulation of esophageal motility, being partly responsible for the latency period and latency gradient between the onset of a swallow and contractions of esophageal circular smooth muscles. Diffuse esophageal spasm appears to be a classical example in which the mechanisms normally responsible for the physiologic timing of the contractions occurring in the esophageal body after swallowing are disturbed. Methods: Five patients (one male and four female; age, 18-48 years) with symptomatic esophageal spasm were given glyceryl trinitrate (GTN) intravenously in gradually increasing doses or L-arginine on two separate occasions and underwent manometric measurements of esophageal motility after wet swallows, using a multilumen perfused catheter system (Synectics Medical, Stockholm, Sweden). The amplitude, duration, and propagation of the contractions and the latency period were analyzed, using specially designed software. Additionally, during the GTN infusion period arterial blood pressure was measured every 5 min. Results: GTN given at a dose of 100 to 200 μg/kg-h intravenously caused the occurrence of and a dose-dependent elongation of the latency period after swallowing. The mean amplitude of the contractions did not show any significant alterations, whereas the mean duration of the contractions decreased significantly, from 11.2±4.8 sec to 5.4 ± 0.8sec. These effects were accompanied by significant alleviation of symptoms during swallowing. Interestingly, no adverse side effects such as headache or flush were observed at any dose of GTN. The blood pressure did not show any changes during the studies in any of the five patients. Administration of L-arginine (300 mg/kg-h intravenously) did not cause any significant alterations of motility pattern or alleviation of dysphagia. Conclusions: 1) NO may play an important role in the control of human esophageal motility, being involved in the mechanisms responsible for the timing of propulsive contractions in the esophageal body after swallowing; 2) GTN may to be of benefit in the treatment of diffuse esophageal spasm in symptomatic patients; and 3) patients with diffuse esophageal spasm may have a malfunction in endogenous NO synthesis and/or degradation.