In a randomized double-blind study, the effect of hypericum extract was compared to that of maprotiline in 24 healthy volunteers. The investigations included measurements of resting EEG as well as visual and acoustic evoked potentials. In resting EEGs, both medications revealed oppositely directed changes in the theta frequencies, and mainly similarly directed changes in alpha and beta frequencies. Measurements of evoked potentials in the theta and beta frequencies supported these results. The results indicate improved cognitive functions mainly with the treatment of hypericum extract.