Hypericum perforatum is used for its beneficial effects on the nervous system, especially as an antidepressant. Owing to the fast-growing St. John's Wort market in the United States, more and more products (herb and extract) are sold at different quality levels. The amount of well-dried H. perforatum plant material is limited and other species with differing composition and no proof of efficacy are sold. The generally used method for standardization--spectrophotometric determination of naphthodianthrones--is not as selective as a high-performance liquid chromatographic (HPLC) method and can be manipulated (eg, by adding colorants). The different analytical methods used for characterization of St. John's Wort are discussed and a combined spectrophotometric and HPLC method is proposed. Qualitative and quantitative ranges for pharmaceutically relevant compounds of St. John's Wort extracts are cited and the composition of European, US, and Far East extracts is detailed. The influence of the production process, which involves extraction solvents, on phytochemical composition is also described.