The main aims of the study are to test if i) EPA enriched n-3 (added to stabilized ongoing treatment) is efficacious in treating depressed patients, but only in subjects with prospectively ascertained elevations in baseline CRP, ii) Changes in inflammatory markers over the course of treatment mediate this effect, and iii) Clinical trial designs utilizing prospectively-ascertained biomarkers to predict response are feasible and thereby pave the way for personalized medicine in psychiatry.