In both animals and humans, stress has been demonstrated to reduce the expression of the Brain-Derived Neurotrophic Factor (BDNF), a neurotrophin (NT) which promotes the proliferation, survival and differentiation of neurons. Although traumatic events have been found to be associated with lower BDNF plasma levels in affective disorders, no study has explored this parameter in patients with post-traumatic stress disorder (PTSD). We, therefore, measured BDNF plasma level in 18 patients with PTSD and in 18 healthy control subjects. Diagnoses were assessed by the Structured Clinical Interview for DSM-IV, while the specific symptoms were examined in the patients by means of the Impact of Event Scale for PTSD and the traumas experienced were assessed by using the Life Events Checklist. BDNF plasma levels were evaluated by means of a standardized Elisa method. The results, while showing significantly lower BDNF levels in PTSD patients, as compared with those of healthy subjects (p=0.001), although obtained in a small sample size, would suggest that this NT may be involved in the pathophysiology of PTSD.