We studied the effect of truncated glucagon-like peptide-1 [naturally occurring GLP-1; proglucagon-(78–107) amide], a potent insulinotropic peptide from the pig ileum, on endocrine and exocrine secretion of potential gastrointestinal target organs using isolated perfused preparations of the porcine pancreas, antrum, and nonantral part of the stomach. Truncated GLP-1 significantly increased somatostatin secretion from the pancreas at 10^-10 mol/liter and more than doubled the secretion at 1O^-9 mol/liter, but had no effect on either somatostatin or gastrin secretion from the antrum or on somatostatin secretion from the nonantral stomach in concentrations up to 10^-8 mol/ liter. Insulin secretion from the pancreas (with 7 mmol/liter glucose in the perfusate) increased 2-fold with truncated GLP-1 at 10^-10 mol/liter and almost 5-fold at 10^-9 mol/liter. Pancreatic glucagon secretion was inhibited by 50% at 10^-10 mol/liter and by 70–80% at 10^-9 mol/liter. Full-length GLP-1 [proglucagon- (72–107)] and GLP-2 [proglucagon-(126–159)] had no effect on hormone secretion from any of the perfused organs. It is concluded that truncated GLP-1 may participate in an enteroinsular control of pancreatic endocrine secretion. (Endocrinology123: 2009–2013,1988)