Patients with mood disorders and healthy volunteers will receive positron emission tomographic (PET) scans with H(2)(15)O to measure global and local differences in cerebral blood flow during a passive introspection task. Patients receive repeated scans while in different mood states and while participating in placebo controlled therapeutic trials as described by separate protocols. Global and regional cerebral blood flow is correlated with data obtained from participation in other protocols, which include clinical (life charting course of illness parameters, mood and anxiety ratings, medication response data, and psychological test performance) and biochemical (levels of medications, monoamines and peptides in the blood and cerebrospinal fluid) measures.