The effect of various carbohydrates on glucagon-like peptide-1 (GLP-1) release was studied in the in vivo perfused rat ileum. GLP-1 concentrations in the mesenteric venous effluent increased significantly after luminal perfusion with substrates of a sodium/glucose cotransporter (d-glucose, d-galactose, methyl-α d-glucoside, and 3-O-methyl-d-glucose). d-Fructose induced a sodium-independent release of GLP-1. Carbohydrates like 2-deoxy-d-glucose and N-acetyl-d-glucosamine, which are not substrates of a luminal sodium/glucose or fructose transporter, did not affect GLP-1 release. Since methyl-α d-glucoside is not a substrate of the basolateral glucose transport mechanism and 3-O-methyl-d-glucose is not metabolized within intestinal cells, it is concluded that intracellular metabolism of carbohydrates and intracellular removal are not essential to induce GLP-1 secretion in rats.