This study is being carried out to see if quetiapine fumarate (Seroquel) is effective in treating bipolar depression during an 8-week acute phase compared with placebo and lithium, followed by continuation treatment for 26 up to 52 with quetiapine fumarate (Seroquel) compared to placebo.

Inclusion Criteria:

• Patients with a diagnosis of bipolar I disorder or bipolar II disorder, currently depressed, aged 18 to 65 years old and outpatient status at enrolment and randomization.

Exclusion Criteria:

• Patients with a current DSM-IV Axis I disorder other than bipolar disorder that is symptomatic or requiring treatment within 6 months of enrolment,
• History of non-response to an adequate treatment
• Patients who, in the investigator's judgment pose a current serious suicidal or homicidal risk
• Pregnancy or lactation
• Clinically relevant disease or clinical finding