PTSD is a serious and debilitating psychiatric disorder that can develop in individuals who were exposed to one or more intense traumatic event(s). Since not all people exposed to traumatic experience develop PTSD, it is assumed that different neurobiological, genetic and environmental risk factors are involved in the vulnerability and/or resilience to PTSD. PTSD biomarkers, defined as characteristics that objectively measure and evaluate normal biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention, might improve the diagnosis and treatment of PTSD. Determined biomarkers were peripheral biochemical markers such as platelet serotonin (5-HT) concentration, platelet monoamine oxidase type B (MAO-B) activity, plasma dopamine-beta-hydroxylase (DBH) activity, and genetic markers /MAO-B intron 13, -1021C/T DBH, catechol-o-methyltransferase (COMT) val158/108met, brain-derived neurotrophic factor (BDNF) val66met, 102T/C serotonin receptor type 2A gene (5HT2A) polymorphism and serotonin transporter (5HTT) gene-linked polymorphic region (5HTTLPR)/. Study participants were Croatian male war veterans with or without current and chronic combat-related PTSD, recruited from the Referral Centre for the Stress-related Disorders of the University Hospital Dubrava, Zagreb. Only plasma DBH activity, but not other markers, differed significantly between war veterans with or without PTSD. When veterans were subdivided according to the narrow clinical symptoms (such as psychotic features, sleep disturbances, suicidal behavior), platelet 5-HT concentration, platelet MAO-B activity, and val66met BDNF were significantly different among these groups. The results indicate that specific PTSD biomarkers, associated with the narrow clinical features, might be indicators of PTSD traits, state or progression, and might be used to improve the diagnosis and treatment of PTSD.