Single-center, randomized, parallel, double-blind, placebo controlled, 8-week trial in subjects with type 2 diabetes mellitus. Two parallel treatment groups include double-blind colesevelam or placebo. A screening period may be up to 18 weeks to withdraw non sulfonylurea antidiabetic treatment or withdraw or adjust sulfonylurea antidiabetic treatment. To evaluate hepatic and peripheral insulin sensitivity, subjects will undergo a two-step hyperinsulinemic-euglycemic clamp with a tritiated glucose infusion at pre randomization and after 8 weeks of treatment. To evaluate oral glucose absorption, subjects will undergo two oral glucose tolerance tests (OGTT) at pre randomization, one without colesevelam and one with colesevelam, and one OGTT at the end of the treatment period..