The purpose of this study is to determine whether quetiapine is effective and safe in the acute treatment of bipolar depression and whether the effect is maintained when treatment is continued.

Inclusion Criteria:

• Male and female out-patients aged 18 to 65 years inclusive
• Diagnosis of Bipolar Disorder (Bipolar I or Bipolar II), most recent episode depressed

Exclusion Criteria:

• Current period of depression lasting less than 4 weeks or more than 12 months
• Use of prohibited medication
• Substance or alcohol dependence or abuse
• Current suicide risk or suicide attempt within 6 months
• Breast feeding or pregnancy
• Clinically relevant disease or clinical finding