Bipolar Depression is a severe illness with high rates of psychiatric comorbidity and increased mortality related to suicide and medical illness. Hypothalamic pituitary axis (HPA) hyperactivity are found in bipolar disorder related to depression and mixed states. Patients with bipolar disorder also have cognitive difficulties and endocrine disturbances may contribute to such dysfunction. Antiglucorticoid therapies are novel treatments of mood disorder. Preliminary data in psychotic depression suggesting that mifepristone (RU-486), a glucocorticoid receptor antagonist, has antidepressant and salutary cognitive effects in a matter of days. In this study we examine the effects of mifepristone in severe bipolar depression in a parallel, double blind placebo controlled experiment. Bipolar subjects maintained on either lithium or valproate, after washout or prior antidepressants have a detailed neuroendocrine assessment. Patients approximately or almost 75 will receive eight days of mifepristone versus placebo after which patients are blindly crossed over to the opposite arm. Patients and a group of matched controls approximately or almost 35 will be compared with neuroendocrine, cognitive, and neurophysiologic testing to fully characterize their phenotype and explore biomarkers of response. It is hypothesized that stigmata of HPA axis hyperactivity and cognitive impairment will be predictive of response to antiglucocorticoid therapy with mifepristone.