• To test the hypothesis that in patients with type 2 diabetes who have not achieved adequate glycemic control with metformin treatment, the addition of exenatide and rosiglitazone will provide superior beta-cell function [ Time Frame: 20 weeks ] [ Designated as safety issue: No ]
  

• Compare the effects of exenatide, rosiglitazone, and a combination of exenatide and rosiglitazone in subjects with type 2 diabetes treated with metformin on various pharmacodynamic measurements and safety and tolerability [ Time Frame: 20 weeks ] [ Designated as safety issue: No ]
  
• Compare total insulin secretion between the exenatide group, rosiglitazone group, and the exenatide plus rosiglitazone group [ Time Frame: 20 weeks ] [ Designated as safety issue: No ]
  

Inclusion Criteria:

• HbA1c of 6.8% to 10.0%, inclusive.
• Body mass index (BMI) of 25 kg/m^2 to 40 kg/m^2, inclusive.

Exclusion Criteria:

• Have participated in this study previously, or have received exenatide, pramlintide acetate, GLP-1 analogs, or dipeptidyl peptidase-IV (DPP-IV) inhibitors
• Have participated in an interventional, medical, surgical, or pharmaceutical study (a study in which an experimental, drug, medical, or surgical treatment was given) within 30 days of study start. This criterion includes drugs that have not received regulatory approval for any indication at the time of study start.

• Treated with any of the following medications:

  • Thiazolidinedione within 5 months of screening;
  • Sulfonylurea within 3 months of screening;
  • Metformin/sulfonylurea combination therapy within 3 months of screening;
  • Alpha-glucosidase inhibitor within 3 months of screening;
  • Meglitinide within 3 months of screening;
  • Insulin for more than 1 week within the 3 months prior to screening.
  • Symlin (pramlintide acetate) injection or Byetta (exenatide) injection at any time
  • Chronic (more than 2 weeks) or recent (within 4 weeks of study start) use of a drug that directly affects gastrointestinal motility
  • Are receiving chronic (lasting longer than 2 weeks) systemic glucocorticoid therapy (excluding topical and inhaled preparations) or have received such therapy within the 4 weeks immediately preceding study start
  • Regular use of a medication with addictive potential such as an opiate, narcotic, or tranquilizer
  • Systemic antineoplastic agent
  • Systemic transplantation medication
  • Drugs for weight loss, including over-the-counter medications, within the 4 months prior to study start