Transcranial direct current stimulation (tDCS) is a selective, painless, brain stimulation technique that allows the electric stimulation of specific cortical regions. TDCS has been recently used as investigational intervention for major depression and treatment resistant depression (TRD) with encouraging results. The present study was aimed to investigate the efficacy and tolerability of tDCS in major depressives with poor response to pharmacological treatment. Twenty-three depressed patients, with a diagnosis of major depressive disorder or bipolar disorder, were treated with augmentative tDCS for 5 days, two sessions per day in a blind-rater trial. The course of depressive symptoms was analyzed using repeated measures ANOVA for HAM-D and MADRS total scores. A qualitative analysis on the basis of the HAM-D response was performed as well. Both analyses were conducted at three time-points: T0 (baseline), T1 (endpoint tDCS) and T2 (end of the first week of follow-up). All patients completed the trial without relevant side-effects. A significant reduction of HAM-D and MADRS total scores was observed during the study (P<0.0001). Treatment response (endpoint HAM-D reduction ≥50%) was obtained by four patients (17.4%) at T1 and by seven patients (30.4%) at T2 and remission (endpoint HAM-D<8) by three patients (13.0%) at T1 and by four subjects (17.4%) at T2. Present findings support the efficacy and good tolerability of tDCS in the acute treatment of patients with TRD with clinical benefit being progressive and extended to the first week of follow-up. Further sham-controlled trials with longer follow-up are needed to confirm present results.