Efficacy of SYR-472 in Subjects With Type 2 Diabetes Mellitus

Inclusion Criteria: * Has a historical diagnosis of type 2 diabetes mellitus. * Has undergone less than 7 days of any antidiabetic therapy except lifestyle modification (diet/exercise) within 8 weeks prior to Screening; or has received metformin monotherapy for at least 8 weeks prior to Screening and maintained a stable daily dose of metformin for at least 12 weeks prior to randomization. * The subject receiving metformin monotherapy at randomization must have been at least 75% compliant with his or her regimen during the Run-in/Stabilization Period as determined by subject diary and investigator assessment. * Has received no treatment with antidiabetic agents other than metformin within the 8 weeks prior to Screening. * Has a glycosylated hemoglobin concentration between 7.0% and 10.0%, inclusive, at Screening and at the Week -1 Visit. * The subject's fasting C-peptide concentration is greater than or equal to 0.8 ng/mL. * Has a fasting plasma glucose concentration less than 275 mg/dL. * If regularly uses other non-excluded medications, must be on a stable dose for at least the 4 weeks prior to Screening. * Has a systolic blood pressure reading less than 160 mm Hg and a diastolic pressure reading less than 100 mm Hg. * Has a hemoglobin value greater than or equal to 12 g/dL for men and greater than or equal to 10 g/dL for women. * Has an alanine aminotransferase level is less than or equal to 3 times the upper limit of normal. * Males have a serum creatinine value less than 1.5 mg/dL; females have a serum creatinine value less than 1.4 mg/dL. * Has a urine albumin/creatinine ratio less than 1000 μg/mg. * Has a thyroid-stimulating hormone level less than or equal to the upper limit of the normal range and is clinically euthyroid. * Females must be not be pregnant or lactating, and must agree to use adequate contraception throughout the duration of the study. * Is able and willing to monitor his or her own blood glucose concentrations with a home glucose monitor. * Has no major illness or debility that in the investigator's opinion prohibits the subject from completing the study. Exclusion Criteria * Is being concurrently treated with antidiabetic therapy other than metformin and lifestyle intervention. * Has a history of cancer, other than squamous cell or basal cell carcinoma of the skin that has not been in full remission for at least 5 years prior to Screening. * Has a history of laser treatment for proliferative diabetic retinopathy within the 6 months prior to Screening. * Has a history of treated diabetic gastric paresis. * Has New York Heart Association class III or IV heart failure regardless of therapy. * Has a history of coronary angioplasty, underwent coronary stent placement or coronary bypass surgery, or suffered a myocardial infarction, or stroke within the 6 months prior to Screening. * Has a history of any hemoglobinopathy that may affect determination of glycosylated hemoglobin. * Has a history of infection with human immunodeficiency virus. * Has a history of a psychiatric disorder that in the investigator's opinion will affect the subject's ability to participate in the study. * Has ingested or received systemically injected glucocorticoids within the 3 months prior to randomization. Inhaled corticosteroids are allowed. * Has used prescription or over-the-counter weight-loss drugs within the 3 months prior to randomization. * Has received any investigational drug within the 30 days prior to Screening or has received an investigational antidiabetic drug within the 3 months prior to Screening. * Has received previous treatment in an investigational study of SYR-472. * Has a known hypersensitivity to any compound related to SYR-472.