In rodents, leptin and the incretin glucagon-like peptide-1 (7-36) amide (GLP-1) affect feeding at least in part via interaction with hypothalamic neuropeptide Y (NPY), suggesting that cross talk may exist between GLP-1 and the ob gene product. Besides insulin, acute hyperglycemia has recently been shown to induce ob gene expression. To address the question of whether leptin plasma levels in humans are affected by GLP-1 infusion and/or hyperglycemia, eight healthy volunteers were studied during euglycemia and hyperglycemic clamping with or without GLP-1 administration while insulin levels were kept constant by somatostatin infusion. Under all conditions, leptin plasma levels remained unchanged, demonstrating that in humans leptin plasma concentrations are affected neither by short-term peripheral GLP-1 infusion nor by hyperglycemia, which suggests that postprandial GLP-1 release and hyperglycemia do not modulate secretion of the ob gene product.