The central action of a plant extract containing hyperici herba flore extractum siccum has been investigated in freely moving rats during a 6 h exposure with two dosages. After frequency analysis of local field potentials electrical power changes of delta waves and alpha2 waves (less pronounced) could be observed within the frontal cortex and hippocampus. As these frequencies are changed predominantly in the presence of drugs acting at the cholinergic or dopaminergic transmitter system, a similar mode of action can be suspected for this plant extract. Despite the fact that statistical significance could only be observed during the fourth hour (p <0.1), the changes induced by the higher dose of the extract containing 1 mg of hypericine were very stable from the 2. to 4. hour after oral application. Classification of the parameters obtained by means of discriminant analysis revealed a trend into the direction of antidepressive EEG drug profiles. Results suggest that quantitative EEG analysis is a very sensitive methodology for the description of pharmacodynamic actions of plant extracts and data can be compared to the action of pure chemical entities.