This study will evaluate the efficacy, safety and tolerability of agomelatine 25 mg or 50 mg per day and will compare agomelatine and paroxetine tolerability. Eligible patients will receive double-blind study medication for 8 weeks. One week after completion of the double-blind treatment phase there will be a single follow-up visit.

Inclusion Criteria:

• Male and female adults, 18 through 70 years of age, inclusive
• Diagnosis of Major Depressive Disorder according to DSM-IV criteria
• HAM-D17 total score > or = 22 at Screening and Baseline

Exclusion Criteria:

• History of non-response to paroxetine
• Patients who have been previously treated with agomelatine
• History of bipolar disorder (I or II), schizophrenia, schizoaffective disorder, eating disorder, or obsessive compulsive disorder
• Any current Axis I disorder other than major depressive disorder which is the focus of treatment
• Substance or alcohol abuse in the last 30 days, dependence in the last 6 months
• Use of any psychoactive medication after the screening visit
• Female patients of childbearing potential who are not using effective contraception

Other protocol-defined inclusion/exclusion criteria may apply