This study will evaluate the safety and efficacy of dutogliptin in patients with type 2 diabetes mellitus (T2DM) who are receiving background therapy of glimepiride with or without metformin.

Inclusion Criteria:

• Type 2 diabetes mellitus, diagnosed at least 3 months prior to Screening (Visit 1)
• BMI 20 to 48 kg/m2, inclusive
• HbA1c 7.0% - 10.0%, inclusive
• Age 18 to 85 years, inclusive

Exclusion Criteria:

• Currently on 3 or more oral antidiabetic drugs or insulin.
• Type 1 diabetes mellitus