This 3-arm study will assess the efficacy, safety and tolerability of taspoglutide compared to insulin glargine in patients with insulin-naive type 2 diabetes mellitus inadequately controlled with metformin and sulphonylurea combination therapy. Patients will be randomized to receive taspoglutide (10 mg once weekly, or 10mg once weekly for 4 weeks followed by 20mg once weekly) or insulin glargine (starting dose 10 IU/day) in a ratio of 1:1:1 in addition to continued prestudy metformin treatment. The anticipated time on study treatment is 2+ years, and the target sample size if 500+ individuals.