Data suggest that both neurotrophic and hypothalamic-pituitary-adrenocortical (HPA) systems are involved in the pathophysiology of depression. The aim of the present study was to investigate whether the non-conservative brain-derived neurotrophic factor (BDNF) Val66Met polymorphism has an impact on HPA axis activity in depressed patients. At admission, the dexamethasone/CRH (DEX/CRH) test was performed in 187 drug-free in-patients suffering from major depression or depressed state of bipolar disorder (DSM-IV criteria). Moreover, genotyping of BDNF Val66Met polymorphism was carried out using the fluorescence resonance energy transfer method (FRET). Homozygous carriers of the Met/Met genotype showed a significantly higher HPA axis activity during the DEX/CRH test than patients carrying the Val/Val or Val/Met genotype (ACTH, cortisol). Our results further contribute to the hypothesized association between HPA axis dysregulation and reduced neuroplasticity in depression and are consistent with the assumption that BDNF is a stress-responsive intercellular messenger modifying HPA axis activity.