Research Design: Over a two year period, 54 patients, male or female, aged 18-30 years who fulfill DSM-IV criteria for schizophrenia or schizoaffective disorder, will be entered into a 12 week, parallel group, double blind, randomized controlled trial assessing the efficacy of placebo vs. DSR (up to 6000 mg/day) augmentation to standard antipsychotic therapy. First episode patients, and patients treated with clozapine, will be randomized separately. Patients will be entered into the trial in accordance with strict inclusion and exclusion criteria after the nature of the study has been explained to them and they have given written informed consent. Clinical evaluations will be performed at baseline and then at regular intervals during the trial. In addition, neurocognitive evaluations, electrophysiological assessments and determination of amino acids levels will be conducted at the beginning and end of the study. Treatment emergent adverse effects will be monitored.