With the predictor problem in mind, we studied in-patients with endogenous depression whether relationships exist among the EEG, the therapeutic response, and the severity of psychopathology. We found that clinically defined responders and non-responders differ in respect of their average power spectra calculated for the two occipital regions. In addition, it was shown that there is a statistically significant correlation between the EEG before treatment and the severity of AMP-documented psychopathology after a 4-week treatment period. This correlation was stronger for the left occipital region than for the right.