The purpose of this study is to help answer the following questions:

• To test if taking LY2599506 for 12 weeks controls blood sugar better than taking placebo for 12 weeks.
• To evaluate the safety of LY2599506 in patients with diabetes.
• To determine if LY2599506 has the ability to control blood sugar in patients with diabetes.
• To determine how much LY2599506 should be given to patients.
• To determine if LY2599506 has an effect on a patient's weight.

The study design consists of 4 study periods: a screening period, a 4-week dose adjustment period, an 8 week treatment period, and a 4-week follow up period.

• Drug: Placebo
  Administered orally for 12 weeks
• Drug: LY2599506
  Administered orally for 12 weeks
  Other Name: Glucokinase Activator

• Placebo twice daily: Placebo Comparator
  Intervention: Drug: Placebo
• 50 mg twice daily LY2599506: Experimental
  Intervention: Drug: LY2599506
• 100 mg twice daily LY2599506: Experimental
  Intervention: Drug: LY2599506
• 200 mg twice daily LY2599506: Experimental
  Intervention: Drug: LY2599506
• 200 mg once daily: Experimental
  Intervention: Drug: LY2599506

Inclusion Criteria:

• Have type 2 diabetes mellitus prior to entering the trial.
• Are currently being treated with diet and exercise therapy consistent with the local standards of medical care.
• May be treated with diet and exercise alone or in combination with a stable of metformin for at least 3 month before entering the trial.
• Have an hemoglobin A1c value between 7.0% and 10.0 %, inclusive.
• Are women not of child-bearing potential due to surgical sterilization (hysterectomy or bilateral oophorectomy or tubal ligation) or menopause. Male patients will be advised to use a reliable method of birth control during the study and until 3 months after the last dose of study medication if their partner is of child-bearing potential.

Exclusion Criteria:

• Use of insulin or any antidiabetic agent other than metformin during the 3 months prior entering the trial.
• Have a gastrointestinal disease that significantly impacts gastric emptying or motility (for example, severe gastroparesis or pyloric stenosis), in the opinion of the investigator, or have undergone gastric bypass or gastric banding surgery.
• Have had more than 1 episode of severe hypoglycemia within 6 months prior to entry into the study, or are currently diagnosed as having hypoglycemia unawareness.
• Have had 2 or more emergency room visits or hospitalizations due to poor glucose control in the past 6 months.
• Have cardiac autonomic neuropathy (for example, resting tachycardia or orthostatic hypotension), based on clinical signs, symptoms, or appropriate diagnostic testing.
• Have cardiac disease with functional status that is New York Heart Association Class II, III or IV or a history of myocardial infarction, unstable angina, or decompensated congestive heart failure in the past 6 month.
• Have poorly controlled hypertension (that is, mean systolic blood pressure of greater or equal than 160 mm/Hg or mean diastolic blood pressure of greater or equal than 100 mm/Hg) history of malignant hypertension, evidence of renal artery stenosis and/or evidence of labile blood pressure including symptomatic postural hypotension. Doses of antihypertensive medications must be stable for 30 days before randomization.
• Have fed or fasting state hypertriglyceridemia (defined as >6.8 mmol/L, 600 mg/dl) at screening. If taking lipid-lowering agents, doses of these medications must be stable for 30 days prior to randomization.
• Have obvious clinical signs or symptoms of liver disease, acute or chronic hepatitis, or repeated alanine transaminase (ALT) levels >2.5 times the upper limit of the reference range at screening.
• Have evidence of a significant active, uncontrolled endocrine or autoimmune abnormality, as judged by the Investigator at screening.
• Have an active or untreated malignancy or have been in remission from a clinically significant malignancy (other than basal or squamous cell skin cancer, in situ carcinomas of the cervix, or in situ prostate cancer) for less than 5 years.