SYR-322 (alogliptin) is a selective, orally available inhibitor of the dipeptidyl peptidase-4 enzyme. Dipeptidyl peptidase-4 enzyme is thought to be primarily responsible for the in vivo degradation of 2 peptide hormones released in response to nutrient ingestion, namely glucagon-like peptide-1 and glucose-dependent insulinotropic peptide. Both peptides exert important effects on islet beta cells to stimulate glucose-dependent insulin secretion as well as regulating beta cell proliferation and cytoprotection. Glucagon-like peptide-1, but not glucose-dependent insulinotropic peptide, inhibits gastric emptying, glucagon secretion, and food intake. Glucose-dependent insulinotropic peptide has been shown to enhance insulin secretion by direct interaction with a glucose-dependent insulinotropic peptide -specific receptor on islet beta cells. The glucose-lowering actions of glucagon-like peptide-1, but not glucose-dependent insulinotropic peptide, are preserved in patients with type 2 diabetes mellitus.