To reveal the genetic determinants of the treatment outcome of escitalopram in depressed patients (by using candidate gene approach and whole genome scanning).

The purposes of this study are:

1. To reveal the genetic determinants of the treatment outcome of escitalopram in depressed patients (by using candidate gene approach and whole genome scanning)
2. To improve the success rate of escitalopram treatment response for depressed patients

Inclusion Criteria:

1. Eligible patients were enrolled in the clinical trials program of hte Samsung Medical Center Geropsychiatry and Affective Disorder Clinics(Seoul, Korea). They received a semistructured diagnostic interview, the Samsung Psychiatric Evaluation Schedule. The affective disorder section of the Samsung Psychiatric Evaluation Schedule uses the Korean version of the structured clinical interview for the diagnostic and statistical manual of mental disorders, Fourth edition.
2. interview with one more patient's family member for objective diagnosis and final diagnosis decision by agreements of two more psychiatric physicians

Exclusion Criteria:

1. received psychotropic medication within 2 weeks of the study or fluoxetine within 4 weeks
2. potential study participants for pregnancy, significant medical conditions, abnormal laboratory baseline values, unstable psychiatric features(eg.suicidal), history of alcohol of drug dependence, seizures, head trauma with loss of consciousness, neurological illness, or concomitant Axis I psychiatric disorder.