Glucagon-like peptide-1 is a peptide hormone from the distal small intestine which stimulates insulin secretion and inhibits glucagon secretion and thereby lowers blood glucose. This hormone, therefore, could be involved in the pathogenesis of postprandial reactive hypoglycemia. We subjected 8 patients showing symptoms of early dumping after partial gastrectomy to an oral 100 g glucose load and measured blood glucose and plasma insulin, C-peptide, glucagon, enteroglucagon and GLP-1 concentrations for 3.5 h after ingestion. Ten matched controls were treated similarly. The patients had higher blood glucose concentrations for the initial 60 min, but lower values for the remaining test period with a nadir of 2.76 +/- 0.19 mmol/l at 146 +/- 17 min after glucose (controls: 3.36 +/- 0.21 mmol/l at 210 +/- 9 min). GLP-1 and enteroglucagon responses were grossly elevated in patients compared to controls and insulin and C-peptide levels were higher during the initial 60 min. Glucagon concentrations increased in patients and decreased in controls. When hypoglycemia occurred, GLP-1 levels were only moderately elevated and insulin and C-peptide levels were lower and glucagon levels higher in patients than in controls. Thus, mechanisms other than release of GLP-1 seem to be responsible for the observed changes in the concentrations of glucose and glucoregulatory hormones.