Abstract
Compared to chemical drugs, the quality control of herbal medicinal products poses many problems due to the complexity of herbal drugs, herbal drug preparations and the products themselves, and due to the use of different analytical methods (selective and non-selective) giving different results. To illustrate this, three groups of herbal medicinal products were assayed by different analytical methods: products containing St. John's wort (colorimetry and HPLC), milk thistle (spectrophotometry and HPLC) and ginkgo (HPLC). These studies show that complete and correct labeling is necessary for the evaluation of herbal medicinal products and that for the majority of plants the knowledge of the applied analytical method is essential for a proper verification of conformity.