The truncated form of glucagon-like peptide-1 (TGLP-1, or proglucagon 78-108), secreted by the mammalian intestine, has potent pharmacological activities, stimulating insulin release and inhibiting gastric acid secretion. We have characterized high-affinity receptors for this peptide in rat isolated fundic glands. Scatchard analysis of binding studies using mono-125I-TGLP-1(7-36) amide as tracer showed a single class of binding site of Kd (4.4 +/- (SE) .08) x 10(-10) M, with a tissue concentration of 1.0 +/- 0.1 fmol sites/microgram DNA. Whole GLP-1 was approximately 700 times less potent in displacing tracer, while human GLP-2 and pancreatic glucagon produced no significant displacement at concentrations up to 10(-6) M. The data support a physiological role for TGLP-1 in the regulation of gastric acid secretion.