This study uses polysomnographs(PSG) to investigate sleep patterns in patients with bipolar depression. This is a double-blind, placebo-controlled, study of ziprasidone that is added to patients current medications. The objective is to relate changes in slow wave and rapid eye movement sleep to changes in mood and overall illness severity. Participants will be randomly assigned to add either placebo or ziprasidone to their current treatment regimen. Participants make 3 to 4 study visits, over a 1 month period, at which they will be asked about their history, mood and sleep quality. Participants will also have three in-home overnight polysomnographs.