Objective. To analyze background EEG parameters correlated with frontal lobe dysfunction, that might be considered, prospectively, as individual predictors of relative pharmacoresistance (or relatively lower treatment efficacy) in different forms of endogenous affective disorders. Material and methods. An analysis of a set of several EEG parameters and quantitative clinical assessments has been carried out during the treatment in patients with endogenous depression (group 1), depressive-delusional conditions in the frames of attack-like schizophrenia (group 2), and manic-delusional conditions in the frames of attack-like schizophrenia (group 3). Results and conclusion. Statistically significant correlations have been revealed between initial (before treatment course) values of narrow-band EEG spectral power (mainly of beta activity reflected the frontal lobe dysfunction and hyper-activation of brain stem structures) and quantitative clinical assessments of patient's conditions at remission stage. The data obtained allow to justify the basic considerations on the brain mechanisms of different affective disorders, and to reveal possible neurophysiologic predictors of relative pharmacoresistance (or relatively lower treatment efficacy) in patients with endogenous affective disorders.