Subjects are excluded if greater than four failed antidepressant trials in the past not including escitalopram (adequate dose and duration) during the index episode of major depression. An adequate trial is defined as 6 weeks of treatment with the antidepressant at a dosage considered therapeutic 159. The doses considered therapeutic are for fluoxetine 20-80 mg/day, paroxetine 20-60 mg/day, sertraline 100-200 mg/day, citalopram 20-40 mg/day, escitalopram 10-20 mg/day, fluvoxamine 100-300 mg/day, bupropion 300-450 mg/day, and venlafaxine 75-375 mg/day.