This 3 arm study will assess the efficacy of taspoglutide on glycemic control (as assessed by HbA1c) in patients with type 2 diabetes mellitus inadequately controlled with metformin plus pioglitazone, compared to placebo after 24 weeks of treatment. Patients will be randomized to one of 3 treatment arms: taspoglutide 10mg once weekly, taspoglutide 20 mg once weekly (after 4 weeks of taspoglutide 10 mg once weekly) or placebo, in addition to their continued stable metformin plus pioglitazone treatment. After the first 24 weeks patients on placebo will be switched to taspoglutide 10mg once weekly or taspoglutide 20mg once weekly (after 4 weeks of taspoglutide 10mg once weekly. The anticipated time on study treatment is 1-2 years, and the target sample size is 100-500 individuals.

Inclusion Criteria:

• adult patients, 18-75 years age;
• type 2 diabetes receiving pioglitazone (>= 30 mg/day) and metformin (>= 1500 mg/day) for at least 12 weeks prior to screening;
• HbA1c >=7.0% and <=10.0% at screening;
• BMI >= 25 (>23 for Asians) and <=45 kg/m2 at screening;
• stable weight +/-5% for at least 12 weeks prior to screening.

Exclusion Criteria:

• history of type 1 diabetes mellitus or acute metabolic diabetic complications such as ketoacidosis or hyperosmolar coma in the previous 6 months;
• evidence of clinically significant diabetic complications;
• clinically symptomatic gastrointestinal disease;
• myocardial infarction, coronary artery bypass surgery, post-transplantation cardiomyopathy or stroke within the previous 6 months;
• known hemoglobinopathy or chronic anemia.