First, the investigators examined the functional relevance of serotonin transporter polymorphisms by quantifying the activity of serotonin transporter in blood platelets of genotyped healthy volunteers and patients with major depression.

Second, the investigators studied response to SSRIs in relation to 5-HTTLPR genotype and also to the functional expression of 5-HTT in platelets.

The purpose of this study is

1. to determine whether serotonin transporter genotypic or functional differences between depressive patients and normal controls were existed.
2. to determine the relationship between serotonin transporter polymorphisms and serotonin transporter functional expression.
3. to determine whether genomic or functional differences between drug responders and nonresponders predict the response of antidepressant

Inclusion Criteria:

• 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.
• interview with one more patient's family member for objective diagnosis and final diagnosis decision by agreements of two more psychiatric physicians

Exclusion Criteria:

• received psychotropic medication within 2 weeks of the study or fluoxetine within 4 weeks
• 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.