Two groups of subjects will be recruited for studies under this protocol: unipolar depressives and bipolar depressives. Subjects with unipolar or bipolar depression appear to exhibit abnormal cholinergic function during the depressed phase, and no differences are hypothesized to exist between MDD and BD depressives herein. However, while BD subjects are more difficult to recruit, the evidence for cholinergic abnormalities has been particularly compelling for BD. Moreover, observations from our pilot study suggest that scopolamine will improve symptoms in both MDD and BD, a particularly persuasive observation given BD notoriously has been difficult to treat. Thus, the magnitude of this serious clinical problem justifies the inclusion of BD subjects. Therefore both groups will be recruited. However, BD Type I subjects will be included only if they are currently stable on lithium or valproate to reduce the risks associated with possible precipitation of mania.