The effect of longstanding therapy using lithium salts compared to other psychotropic drugs in combination with lithium salts or other psychotropic drugs alone, on the human EEG is examined and compared with the literature. We found in our sample of 56 patients under lithium therapy: (1) that lithium salts - like other psychotropic drugs - evoke a significant increase in paroxysmal dysrhythmic activity and EEG abnormalities collectively; (2) that lithium salts cause an increase in rhythmical patterns and abnormalities in vigilance; and that (3) the combination of lithium salts with other psychotropic drugs leads to a significant augmentation of focal abnormalities of the left brain area and epileptic potentials, while EEG recordings without abnormalities are significantly diminished under this therapy. It results from this investigation that the risk for central decompensation in relation to the individual disposition seems to be especially high for the combination therapy.