Hypofunction of N-methyl-D-aspartate (NMDA) receptor has been implicated in the pathophysiology of schizophrenia. To date, several reported trials on adjuvant NMDA-enhancing agents, including glycine and sarcosine (a glycine transporter I inhibitor), demonstrated clinical benefits for schizophrenia patients. This project aims to compare the efficacy and safety of sarcosine and combination of sarcosine and BE, as adjunctive therapy for schizophrenia, and to explore the possible synergistic effects of them. Sixty chronic schizophrenic inpatients will be enrolled in the 12-week double-blind, placebo-controlled trial. The participants receive stable antipsychotic regimens concomitant with sarcosine (2 g/d) (N=21), sarcosine(2 g/d) + BE(1 g/d ) (N=21), and placebo(N=21). Measures of clinical efficacy and side-effects were determined every 3 weeks. Measures of cognitive function were determined at the beginning and the end of the study. The efficacies of three groups are compared, and the characteristics of better responders are analyzed.