Saint-John’s-wort (Hypericum perforatum L.) has been used in traditional medicine since time immemorial and it has its position also in the contemporary list of medicinal plants of pharmaceutical importance. Though it originally comes from Europe and Asia, it has been domesticated and, thanks to its properties, has been cultivated in many other parts of the world. The herbaceous plant contains a wide spectrum of substances, out of which anthraglycosides, flavonoids, and floroglucin derivatives participate in principal pharmacological effects. In recent years this plant has become greatly popular as an effective alternative means for the treatment of weak to medium forms of depression. Large quantities of mass-produced drugs with its extract are sold mainly in the United States and Germany and successfully penetrate into the markets of other European countries including the Czech Republic. Some adverse side-effects are also connected with the plant, the best known being photosensitivity, lesser known being its interactions with other drugs or foodstuffs.The present review aims to process literary references concerning the biological activities of the plant and point out its most important therapeutic and toxicological aspects.

        Key words: Hypericum perforatum L. – pharmacology – depression – photosensitivity