Analysis of EEG spectral power values and quantitative clinical scores of depressive conditions has been carried out in the dynamics of the treatment of 40 patients with endogenous depression, with the main goal to study the neurophysiological correlates and to search for possible predictors of therapeutic out come. The reduction of depressive symptoms by the end of the treatment course was associated with EEG signs of improvement of the brain's functional state. Significant correlations have been revealed between the EEG narrow band spectral power values and clinical scores. As well, significant correlations have been revealed between some initial (before the beginning of the treatment) EEG parameters and quantitative clin ical scores at the initial stage of remission. The values of EEG β 1 and β 2 spectral power appeared to be pre dictors, while initially larger values of EEG spectral power were associated with the high manifestation of residual depressive symptoms after the treatment. The results support the basic views on the brain's mecha nisms of various aspects of depressive disorders and reveal the possible neurophysiological predictors of the efficacy of the treatment of endogenous depression.