Utilizing quantitative analysis of the human electroencephalogram (EEG), the effect of typical and atypical antidepressants on the central nervous systems (CNS) was studied in several double-blind, placebo-controlled trials. At least two types of pharmaco-EEG profiles may be differentiated: 1) a thymeretic, desipramine-like pharmaco-EEG profile suggesting activating properties of the drug (desipramine, tranylcypromine, nomifensine, higher doses of pirlindol and to some extent of fluoxetine); 2) a thymoleptic imipramine- and amitriptyline-like pharmaco-EEG profile showing also sedative qualities (imipramine, amitriptyline, maprotiline, binodaline, danitracene and fluvoxamine). A small number of new compounds exhibit still another pharmaco-EEG profile which may reflect some activating properties different from the above-described ones (clovoxamine, ciclopramine, tandamine). Trazodon on the other hand, produced just opposite changes indicating sedative effects. Aside from determining the type of EEG changes, the pharmaco-EEG method seems to be of value in determining time- and dose-efficacy relations at the target organ--the human brain. The relationships between pharmacodynamics and pharmacokinetics will be discussed.