The aim of this study is to asses the effects of the NMDA receptor full agonist D-serine while used as adjuvant treatment for individuals suffering from chronic posttraumatic stress disorder (PTSD). Dysfunction of neurotransmission mediated at NMDA receptor plays a cardinal role in the pathophysiology of PTSD and PTSD patients typically suffer from cognitive dysfunctions and avoidance& depressive symptomatology that may be mediated by NMDA receptor function deficits.