The phenomenon that oral glucose elicits a higher insulin response than does intravenous (iv) glucose, even at identical plasma glucose (PG) profiles (isoglycemia), is called the incretin effect. In type 2 diabetes mellitus (T2DM) the incretin effect has been shown to be markedly reduced or even abolished. It is not known whether the reduced incretin effect in T2DM is a primary event leading to T2DM or if it is merely a consequence of the diabetic state. To answer this question the investigators plan to estimate the incretin effect in 8 patients with secondary diabetes mellitus (DM) to chronic pancreatitis (CP) and compare it to the incretin effect of 8 patients with CP and normal glucose tolerance (NGT). Eight patients with T2DM and 8 healthy control subjects are studied for comparison. The incretin effect is measured by a 50-g oral glucose tolerance test and an isoglycemic intravenous glucose infusion.