Dipeptidyl peptidase-IV (DPP-IV) is involved in the inactivation of glucagon-like peptide-1 (GLP-1), a potent insulinotropic peptide. Thus, DPP-IV inhibition can be an effective approach to treat type 2 diabetes mellitus by potentiating insulin secretion. This study describes the biological effects of a new DPP-IV inhibitor, KR-62436 (6-{2-[2-(5-cyano-4,5-dihydropyrazol-1-yl)-2-oxoethylamino]ethylamino}nicotinonitrile) in vitro and in vivo. KR-62436 inhibited rat plasma DPP-IV, porcine kidney DPP-IV as well as human DPP-IV (Caco-2) with IC50 values of 0.78, 0.49, 0.14 microM, respectively. In addition, the compound (10 microM) almost completely inhibited DPP-IV-mediated degradation of GLP-1 in vitro. KR-62436 inhibited the enzyme in a competitive manner, and exhibited selectivity against several proteases including proline-specific proteases. In vivo efficacy of the compound was examined by using normal C57BL/6J mice and ob/ob mice, a type 2 diabetes animal model. Administration of KR-62436 to C57BL/6J mice either orally or subcutaneously resulted in the suppression of plasma DPP-IV activity, increase in intact GLP-1 and insulin levels in plasma. Furthermore, the plasma glucose concentrations during oral glucose tolerance test (OGTT) were reduced upon oral administration of KR-62436. This study demonstrates that KR-62436 could be a good lead compound for further development as a new anti-diabetic agent.