- Treatment-resistant bipolar depressive disorder without psychosis and a MADRS baseline score of >20. All patients must have history of being on a serum-verified (at time of entry into study) mood stabilizer [lithium at 0.5-1.2mEq/L; or valproic acid, 50-125mcg/ml] for 4 weeks prior to entry into the study and remain on this mood stabilizer during the course of the trial. Further, subjects will have failed two adequate dose/duration antidepressant courses in their lifetime, including one in the current depressive episode (verified by Antidepressant Treatment History Form).