We investigated how various types of gastric surgery influenced the effect of peptone on the lower esophageal sphincter (LES) (12 healthy volunteers, 10 patients following selective proximal vagotomy (SPV), 10 patients following Billroth I (B I), 10 patients following Billroth II (B II) and 10 patients following ⅔ resection and Roux-en-Y reconstruction). On two separate occasions we measured the LES response to the intragastral application of either 300 ml 0.9% saline or 300 ml 20% peptone solution from 15 min before to 60 min after instillation. The resting pressures in patients with SPV, B II or Roux-en-Y were significantly (p < 0.05) lower than those in the volunteers or patients with B I. Peptone causes a physiological LES pressure (LESP) increase only in healthy volunteers or in patients with SPV. After all gastric resection procedures the LESP decreases in response to peptone stimulation. There is no correlation with the maintenance of the duodenal passage. It appears, rather, that the destruction of the vagal connections from the duodenum to the LES is the reason for the pressure decrease.