- Refractory depression is a highly debilitating mental condition that originates major social and economic burden. About 50% of the patients experience a chronic course of illness and up to 20% show an insufficient response to drug treatments. Electroconvulsive therapy (ECT) is the most effective treatment method in refractory depression, although its mechanism of action is still unknown. Brain-derived neurotrophic factor (BDNF) is decreased in depressive episodes, and increases with antidepressant treatment, being suggested as a biomarker of response to ECT. We report the findings of a study on the effects of ECT on BDNF and clinical outcomes in a group of drug resistant depressive patients before and after ECT. The patients post-ECTs have shown an important improvement of depressive symptomatology on the HDRS (p=0.001), of psychotic features on the BPRS (p=0.001) and of the severity of illness on the CGI (p=0.001). There were no changes in the serum BDNF before and after the ECT treatment (p=0.89). These results do not support the hypothesis that the clinical improvement following ECT is due to changes in the BDNF.