A Study to Compare the Effects of Exenatide and Sitagliptin on Postprandial Glucose in Subjects With Type 2 Diabetes Mellitus

Inclusion Criteria: * Treatment with metformin for at least 2 months * Has HbA1c 7.0% to 11.0%, inclusive, at screening * Body mass index (BMI)25 kg/m\^2 to 45 kg/m\^2, inclusive * List of medications that are not allowed or the patient has been on stable treatment for at least 2 months: * Hormone replacement therapy (female subjects) * Oral contraceptives (female subjects) * Antihypertensive agents * Lipid-lowering agents * Thyroid replacement therapy Exclusion Criteria * Has been treated with exenatide (BYETTA®) or any DPP-4 inhibitor prior to screening * Received any study medication or participated in any type of clinical trial within 30 days prior to screening * Has donated blood within 60 days of screening visit or is planning to donate blood during the study * Treated with any of the following medications: * Sulfonylurea or Thiazolidinedione within 3 months of screening; * Alpha-glucosidase inhibitor, meglitinide, nateglinide, or pramlintide (SYMLIN®)within 30 days of screening; * Insulin within 2 weeks prior to screening or insulin for longer than 1 week within 6 months of screening; * Drugs that directly affect gastrointestinal motility, including but not limited to, anticholinergics, macrolide antibiotics, dopamine antagonists, opioids, and Reglan®(metoclopramide); * Systemic corticosteroids by oral, intravenous, or intramuscular route; or potent, inhaled, or intrapulmonary (including ADVAIR®) steroids known to have a high rate of systemic absorption;