This study will compare the effects of 2.0 mg exenatide once weekly injection as monotherapy to 3 active comparators(metformin, dipeptidyl peptidase-4 inhibitor, and thiazolidinedione) in drug naive patients with type 2 diabetes treated with diet and exercise.

• Drug: exenatide once weekly
  subcutaneous injection, 2mg, once weekly
• Drug: metformin
  oral, 1000-2500mg, daily
• Drug: sitagliptin
  oral, 100 mg, daily
• Drug: pioglitazone
  oral, 30-45mg, daily

• 1: Experimental
  Intervention: Drug: exenatide once weekly
• 2: Active Comparator
  Intervention: Drug: metformin
• 3: Active Comparator
  Intervention: Drug: sitagliptin
• 4: Active Comparator
  Intervention: Drug: pioglitazone

Inclusion Criteria:

• have type 2 diabetes and are treated with diet and exercise alone.
• at least 18 years of age.
• HbA1c between 7.1% and 11.0%, inclusive.
• Body mass index (BMI) of 23 kg/m2 to 45 kg/m2, inclusive.
• Have a history of stable body weight (not varying by >5% for at least 3 months prior to screening).

Exclusion Criteria:

• Have history of cardiac disease or presence of active cardiac disease within the year prior to inclusion in the study including myocardial infarction, clinically significant arrhythmia, unstable angina, moderate to severe congestive heart failure, coronary artery bypass surgery, or angioplasty
• Have a history of renal transplantation or are currently receiving renal dialysis
• Have active or untreated malignancy, or have been in remission from clinically significant malignancy (other than basal cell or squamous cell skin cancer, in situ carcinomas of the cervix, or in situ prostate cancer) for less than 5 years.
• Have history of severe GI disorder (e.g., gastroparesis)
• Have a history of acute or chronic pancreatitis.
• Have active proliferative retinopathy.
• Have been treated with drugs that promote weight loss (e.g., Xenical®[orlistat], Meridia® [sibutramine], Acomplia® [rimonabant], Acutrim® [phenylpropanolamine], or similar over-the-counter medications) within 3 months of screening.
• Have been treated with any antidiabetic agent for more than 7 days within 3 months prior to screening.
• Have had an organ transplant.
• Have previously completed or discontinued study drug in this study, withdrawn from this study or any other study investigating exenatide once weekly.
• Have received treatment within the last 30 days with a drug that has not received regulatory approval for any indication at the time of study entry.
• Are currently enrolled in any other clinical study.