The primary objective of the study is to compare, after 8 weeks, the efficacy of SR58611A vs. placebo in patients with Major Depressive Disorder who are on concomitant treatment with escitalopram.

The secondary objective of this study is to document clinical safety and tolerability of SR58611A in association with escitalopram.

Inclusion Criteria:

• Inpatients or outpatients with Major Depressive Disorder characterized by a recurrent Major Depressive Episode with Montgomery and Asberg Depression Rating Scale (MADRS) total score => 30

Exclusion Criteria:

• Patient is at immediate risk for suicidal behavior
• Patient with psychotic features, catatonic features, seasonal pattern or postpartum onset
• Patients with a current depressive episode secondary to a general medical disorder
• Patients with a lifetime history or presence of bipolar disorder, psychotic disorder, panic disorder and antisocial personality disorder
• Patients with severe or unstable concomitant medical conditions
• Pregnant, breastfeeding, or likely to become pregnant during the study
• Treated with escitalopram within 6 months before the study, or who have had an adverse reaction to escitalopram

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