Hypothesis 3: After patients who have had inadequate antidepressant responses to SSRI treatment complete six weeks of augmentation with placebo, or with .7 grams or 1.5 grams per day of EPA, a relationships will exist between final MADRS scores and both the final RBC concentrations of DHA and EPA and the final RBC ratio of AA to EPA. These relationships will resemble those between baseline RBC concentrations and subsequent responses to escitalopram and will suggest therapeutic ranges for these concentrations.