This 3-arm study will assess the efficacy, safety and tolerability of taspoglutide compared with exenatide in patients with type 2 diabetes mellitus inadequately controlled with metformin, thiazolidinedione or a combination of both. Patients will be randomized to receive taspoglutide (10mg once weekly or 10mg once weekly for 4 weeks followed by 20mg once weekly) or exenatide (5 micrograms twice daily for 4 weeks followed by 10 micrograms twice daily) in a ratio of 1:1:1 in addition to continued prestudy metformin and thiazolidinedione either alone or in combination. The anticipated time on study treatment is 3+ years, and the target sample size is >500 individuals.

Inclusion Criteria:

• adult patients, 18-75 years of age;
• type 2 diabetes receiving metformin and/or pioglitazone or rosiglitazone for at least 12 weeks;
• HbA1c >=7.0% and <=10% at screening;
• BMI >=25kg/m2 (>23kg/m2 for Asians) and <=45kg/m2 at screening;
• stable weight +/- 5% for at least 12 weeks prior to screening.

Exclusion Criteria:

• history of type 1 diabetes, diabetes resulting from pancreatic injury or secondary forms of diabetes;
• history of acute metabolic diabetic complications within the previous 6 months;
• evidence of clinically significant diabetic complications;
• known proliferative diabetic retinopathy;
• myocardial infarction (MI), coronary artery bypass surgery, post-transplantation cardiomyopathy (PTCM) or stroke within the past 6 months;
• any abnormality in clinical laboratory test or ECG, which precludes safe involvement in the study as judged by the investigator;
• known hemoglobinopathy or chronic anemia;
• clinically significant gastrointestinal disease.