The purpose of this study is to determine the efficacy of quetiapine compared to placebo in the treatment for a major depressive episode in patients with bipolar disorder after receiving treatment for up to 8 weeks.

Inclusion Criteria:

• Provision of informed consent before enrollment and any study-specific procedures. Patients deemed incapable of providing written consent will not be enrolled in this study; outpatient status

Exclusion Criteria:

• More than 8 mood episodes in the past year from screen (visit 1);
• A current Axis I disorder other than bipolar disorder within 6 months of screening;
• patients with clinically significant abnormal laboratory findings in the investigator's judgment