This study is a 12-week, double-blind, placebo-controlled trial of L-methylfolate 15 mg/d supplementation in schizophrenia patients with mild or greater negative symptoms. L-methylfolate, a prescription medical food, is the activated form of folate required for conversion of homocysteine to methionine and hence is the optimal form of folate for supplementation, since it eliminates the need for activation by MTHFR. The purpose of this study is to examine the change in plasma L-methylfolate concentrations following a three-month trial of L-methylfolate 15 mg/d compared to placebo.