males or females age 18-70 years

type 2 diabetes mellitus for ≥ 6 months prior to screening visit 1

on a stable (> 3 months prior to screening visit 1) treatment regimen of metformin monotherapy;

fasting plasma glucose < 240 mg/dl at screening visit 1

hba1c ≥ 7% and ≤ 10% at screening visit 1

prior treatment with exenatide

treatment with any of the following antidiabetic agents within 3 months prior to screening visit 1: tzds, sulfonylureas, dpp iv inhibitors, acarbose, or insulin (injected or inhaled)

history of type 1 diabetes and/or history of diabetic ketoacidosis

body mass index ≥ 40 kg/m2;

history of organ transplantation