The aqueous extracts from 178 kinds of medicinal plants belonging to 69 families were examined from the point of their virustatic activity against herpes-, influenza-, vaccine- and poliovirus. 75 kinds proved to be virustatic against one or more kinds of virus. Nearly one-third of the active plants belong to families that are known as especially rich in tannin. Besides the virustatic activity a great number of extracts showed also a cytostatic activity.