The purpose of the study is to evaluate the efficacy of SSR149415 in the treatment of Major Depressive Disorder, defined as a change from baseline to visit 7 in the Hamilton Depression Rating Scale.

To evaluate the tolerability, safety and efficacy on disability and quality of life in patients with major depressive disorder.To evaluate plasma concentrations of SSR149415.

Inclusion Criteria:

• Diagnosis of major depressive disorder, recurrent, as defined by Diagnostic and Statistical Manual of Mental Disorders, 4th edition, Text Revision (DSM-IV-TR) criteria (296.3) and confirmed by the semi-structured Mini International Neuropsychiatric Interview (MINI)

Exclusion Criteria:

• Total score of less than 24 on the MADRS.
• HAM-D total score less than 18.
• Duration of the current depressive episode less than 1 month or greater than 2 years.
• Patients with a history or presence of bipolar disorders or psychotic disorders.
• Patients with alcohol dependence or abuse or substance dependence or abuse in the past 12 months except nicotine or caffeine dependence.
• Patients who have used the following prior to entry into Acute Phase: antipsychotics within 3 months, fluoxetine within 1 month, MAOIs within 2 weeks, other antidepressants, or mood-stabilizer (lithium, anticonvulsants) within 1 week.

The investigator will evaluate whether there are other reasons why a patient may not participate