Background: Pharmacological treatment of depression is currently led by the trial and error principle mainly because of lack of reliable biomarkers. Earlier fi ndings suggest that baseline alpha power and asymmetry could diff erentiate between responders and non-responders to specifi c antidepressants. Aim: The current study investigated quantitative electroencephalographic (QEEG) measures before and early in treatment as potential response predictors to various antidepressants in a naturalistic sample of depressed patients. We were aiming at developing markers for early prediction of treatment response based on diff erent QEEG measures. Materials and methods: EEG data from 25 depressed subjects were acquired at baseline and after one week of treatment. Mean and total alpha powers were calculated at eight electrode sites F3, F4, C3, C4, P3, P4, O1, O2. Response to treatment was defi ned as 50% decrease in MADRS score at week 4. Results: Mean P3 alpha predicted response with sensitivity and specifi city of 80%, positive and negative predictive values of 92.31% and 71.43%, respectively. The combined model of response prediction using mean baseline P3 alpha and mean week 1 C4 alpha values correctly identifi ed 80% of the cases with sensitivity of 84.62%, and specifi city of 71.43%. Conclusions: Simple QEEG measures (alpha power) acquired before initiation of antidepressant treatment could be useful in outcome prediction with an overall accuracy of about 80%. These fi ndings add to the growing body of evidence that alpha power might be developed as a reliable biomarker for the prediction of antidepressant response.