This is an open-label study assessing the efficacy of l-methylfolate as monotherapy in patients with mild to moderate major depressive disorder (MDD). The plan is to enroll 75 patients with mild to moderate MDD based on the Structured Clinical Interview for DSM-IV (SCID) that have a Hamilton Depression Rating Scale-24 (HDRS-24) score between 8-24. The investigators will collect genotype data on methylenetetrahydrofolate Reductase (MTHFR), MTR and MTRR in this patient population. Subjects will be able to receive their genotype results, on request, upon completion of the study. The investigators hypothesize that depressed patients will be more likely to have a mutation in the MTHFR gene