Hyperici Oleum (St. John's wort oil) used in wound healing contains no hypericin. By using the sunlight maceration method described in the supplement to DAB 6 (EB 6), lipophilic breakdown products of this compound are obtained which lend the oil its red colour. Hyperforin, which is responsible for the oil's therapeutic activity could, for the first time, be identified and quantitatively determined by TLC and HPLC after solid-phase extraction. The stability of hyperforin is limited; sufficient shelf-life could only be achieved by hot maceration of dried flowers with eutanol G and storage in the absence of air. By gradient HPLC further polar hyperforin analogues were detected in those St. John's wort oils in which hyperforin had decomposed. At the same time flavonoids and xanthones could be identified. A procedure for the quantitative determination of flavonoids in St. John's wort was validated. The action of light during preparation of the oil led to a rise in the content of flavonoids.