SYR-322 (alogliptin) is a selective, orally available inhibitor of dipeptidyl peptidase IV currently in development by Takeda Global Research & Development Center, Inc. as a treatment for type 2 diabetes mellitus. Dipeptidyl peptidase IV is the primary enzyme involved in the in vivo degradation of at least 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 β-cells to stimulate glucose-dependent insulin secretion and regulate β-cell proliferation and cytoprotection. Glucagon-like peptide-1 also inhibits gastric emptying, glucagon secretion, and food intake. The glucose-lowering actions of glucagon-like peptide-1, but not glucose-dependent insulinotropic peptide, are preserved in patients with type 2 diabetes.