Inclusion criteria:

At screening:

• Patients with type 2 diabetes mellitus, as defined by WHO (fasting plasma glucose > or = 7 mmol/L (126mg/dL) or 2 hours postprandial plasma glucose > or = 11.1 mmol/L (200 mg/dL), diagnosed at least 1 year before the screening visit
• For at least 3 months: treatment with a stable dose of metformin > or = 1.5 g/day or combination of stable doses of metformin > or = 1.5 g/day with sulfonylureas (SUs) (to be stopped at the run-in visit (V2)) and/or Thiazolidinediones (TZDs)
• Glycated hemoglobin (HbA1c) > or = 7.0 and < or = 10%

At the end of the run in phase and before randomization:

• HbA1c > or = 7.0 and < or = 9%
• Mean fasting Self Monitored Plasma Glucose (SMPG) calculated from the self measurements for the 7 days prior to visit 12 (week -1) is less than or equal to 140 mg/dll (7.8 mmol/l)

Exclusion criteria:

At screening:

• Pregnancy or lactation
• Women of childbearing potential with no effective contraceptive method.
• Type 1 diabetes mellitus
• Metformin not at a stable dose of at least 1.5 g/day for at least 3 months prior to the screening visit.
• Use of oral or injectable antidiabetic or hypoglycemic agents other than metformin, sulfonylurea and thiazolidinediones within 3 months prior to the time of screening, use of weight loss drugs if not at a stable dose for at least 3 months prior to the screening visit.
• History of hypoglycemia unawareness.
• History of unexplained pancreatitis, chronic pancreatitis, pancreatectomy, stomach/gastric surgery, inflammatory bowel disease
• History of metabolic acidosis, including diabetic ketoacidosis within 1 year prior to screening
• Hemoglobinopathy or hemolytic anemia, blood or plasma products transfusion within 3 months prior to the time of screening
• Within the last 6 months prior to screening: history of myocardial infarction, stroke, or heart failure requiring hospitalization
• Known history of drug or alcohol abuse within 6 months prior to the time of screening
• Uncontrolled or inadequately controlled hypertension at the time of screening with a resting systolic or diastolic blood pressure > 180 mmHg or > 110 mmHg, respectively
• Use of systemic glucocorticoids (excluding topical application or inhaled forms) for one week or more within 3 months prior to the time of screening
• Use of any investigational drug within 3 months prior to screening
• Renal impairment defined with serum creatinine > 1.4 mg/dL in women and > 1.5 mg/dL in men
• History of hypersensitivity to insulin glargine or to any of the excipients
• Clinically relevant history of gastrointestinal disease associated with prolonged nausea and vomiting, including (but not limited to): gastroparesis, unstable (i.e worsening) and not controlled (i.e prolonged nausea and vomiting) gastroesophageal reflux disease requiring medical treatment, within 6 months prior to the time of screening
• Any previous treatment with lixisenatide (e.g. participation in a previous study with lixisenatide)
• Allergic reaction to any GLP-1 receptor agonist in the past (e.g. exenatide, liraglutide) or to metacresol

Additional exclusion criteria during or at the end of the run-in phase before randomization :

• Informed consent withdrawal (patient who is not willing to continue or fails to return)
• Mean fasting SMPG calculated from the self-measurements for the 7 days prior to visit 12 (week -1) is > 140 mg/dl (7.8 mmol/l)
• HbA1c measured at visit 12 (week -1) is < 7% or > 9 %,
• Amylase and/or lipase > 3 times the upper limit of the normal laboratory range at visit 12 (week -1)

The above information is not intended to contain all considerations relevant to a patient's potential participation in a clinical trial.