The purpose of the study is to investigate whether eight weeks of treatment with flexible doses of Bifeprunox is superior to treatment with placebo in depressed patients with bipolar disorder.

Inclusion Criteria:

• Men and women 18 to 65 years of age, inclusive.
• Diagnosis of Bipolar Disorder and must be experiencing a depressive episode.

Exclusion Criteria:

• This is a follow on study to protocol 3168A2-304. Only subjects who have participated in the previous study are eligible.