Linagliptin is a xanthine-based dipeptidyl peptidase (DPP)-4 inhibitor that is now available in numerous countries worldwide for the treatment of type 2 diabetes mellitus (T2DM). The aim of this study was to evaluate further the mechanisms underlying the improvements in glycemic control observed with linagliptin. The effects of linagliptin on DPP-4, pharmacodynamic parameters, and glycemic control versus placebo were assessed in patients with inadequately controlled T2DM.