 For the group with significant anhedonia, current MDD, as defined by DSM-IV criteria, with significant anhedonia defined as having PAS andor SAS scores at or above one standard deviation of appropriate norm. For the group without significant anhedonia, current MDD, as defined by DSM-IV criteria, without significant anhedonia defined as having PAS andor SAS scores within or below one standard deviation of appropriate norm. The BPD subjects will meet DSM-IV criteria for bipolar I or II disorder, most recent episode depressed and will currently be in a major depressive episode. We will use the Young Mania Rating Scale to assess the severity of the disorder Subjects may be enrolled as either inpatients or outpatients at their entrance to the study. 