Recently a new therapeutic concept using DPP IV inhibitors in combination with metformin has been introduced in the treatment of type 2 diabetic patients. There is some evidence that, in the beta cell, DPP IV Inhibitors might improve the conversion of intact Proinsulin into Insulin and C-peptide and thereby reduce circulating intact proinsulin levels. Since the number of type 2 diabetic patients treated with DPP-IV inhibitors is steadily increasing, there is a need to generate more data on the postprandial release of intact proinsulin in patients treated with DPP-IV inhibitors compared to Insulin or sulfonylurea treatment.