Relapse and recurrence are common following successful short-term treatment of unipolar depression. Evidence from a number of controlled double-blind investigations indicates that a patient with a history of depressive episodes is best protected against future episodes by being maintained on the same antidepressant agent at the same dose that was used to treat the acute episode. Newer agents, such as paroxetine, sertraline, and fluoxetine, have been studied in controlled manner for up to one year. The effectiveness of the SSRI in preventing recurrence of depression has been well established in six investigations.