The overall aim of the proposed project is to assess the efficacy and safety of the N-methyl-D-aspartate glutamate receptor (NMDAR) modulator, glycine transport inhibitor sarcosine (N-methylglycine) for the treatment of individuals fulfilling schizophrenia prodromal syndromes criteria. NMDAR's dysfunction plays a cardinal role in schizophrenia pathophysiology and the establishment of neurodevelopmental deficits. During the last decade it was demonstrated that pharmacological treatment with compounds that enhance NMDAR-mediated neurotransmission due to their agonistic activity at the NMDAR-associated glycine site (e.g. glycine, D-serine) leads to significant symptom reductions in chronic schizophrenia patients. Furthermore, preliminary findings suggest that glycine treatment may also be beneficial for patients at high risk for developing schizophrenia. By increasing glycine synaptic levels, sarcosine may generate improved therapeutic effects in high risk individuals. Sarcosine is a natural amino acid that has already been shown to reduce positive, negative and cognitive symptomatology in chronic as well as acute schizophrenia patients. Advantages of sarcosine vs. glycine site agonists use include the relatively low dose required and the lack of known side effects. Synthetic compounds conceptually similar to sarcosine are presently in various stages of development by major pharmacological companies.