To evaluate the efficacy of quetiapine fumarate sustained release (Seroquel SR™) in combination with an antidepressant versus an antidepressant alone in patients with Major Depressive Disorder.

PLEASE NOTE: Seroquel SR and Seroquel XR refer to the same formulation. The SR designation was changed to XR after consultation with FDA.

Inclusion Criteria:

• Male or female aged 18 to 65 years
• A documented diagnosis of major depressive disorder

Exclusion Criteria:

• Patients with a DSM IV Axis I disorder other than MDD within 6 months of enrolment
• Patients with a diagnosis of DSM IV Axis II disorder which has a major impact on the patient's current psychiatric status
• Patients whose current episode of depression exceeds 12 months or is less than 4 weeks prior to enrolment