 The study was approved by the UCSF Committee on Human Research, and all participants gave informed consent. The depressed subjects began treatment with placebo for one week, followed by escitalopram for eight weeks 10 mg per day x 4 weeks, followed by 20 mg per day x 4 weeks, as tolerated in a double-blind, fixed-order, within-subject cross-over manner. The depressed subjects and the psychiatric rater were unaware of the study design and the sequence and duration of treatments. Depressed and control subjects underwent venipuncture to obtain blood for assays. The controls underwent venipuncture once, and the depressed subjects had venipuncture just prior to beginning active escitalopram treatment and again after 8 weeks of escitalopram treatment. Blood was also collected at Weeks 4 and 8 of treatment in the depressed subjects for assay of citalopram and citalopram metabolites, to gauge medication compliance. Finally, depression severity and global clinical change were assessed in the depressed subjects at Baseline and at the end of Week 8 of escitalopram treatment. 