We studied the effect of gastrin-17 on lower esophageal sphincter (LES) characteristics in man. Nine healthy volunteers participated in two experiments performed in random order during continuous infusion of saline (control) or gastrin-17 (15 pmol/kg/hr). LES pressure (LESP) and transient lower esophageal sphincter relaxations (TLESR), as most the important reflux mechanism, were measured with intraesophageal sleeve manometry combined with pH metry. Infusion of gastrin-17 resulted in plasma gastrin levels comparable to those reached after a mixed meal. During continuous gastrin infusion, LESP decreased significantly (P < 0.05) compared to control. The rate and duration of TLESR was not influenced by gastrin-17. Gastroesophageal reflux and the number of TLESR associated with reflux were significantly (P < 0.05) increased during gastrin infusion. These results suggest that in humans gastrin at physiological postprandial plasma concentrations decreases LESP, does not influence TLESR, but increases the percentage of TLESR associated with reflux.