Establishing the pharmacological basis for efficacy of herbal medicinal products (HMPs) is a continuous challenge. In this context, also the question of bioavailability, the elucidation of metabolic pathways and their pharmacokinetics is of major interest. These data are relevant to link results from pharmacological IN VITRO assays and clinical studies. A better understanding of the pharmacokinetics and bioavailability of phytopharmaceuticals can also help in designing rational dosage regimes. The preparations used in the present pharmacokinetic single-dose study are different ECHINACEA PURPUREA formulations (Echinaforce) with various excipients. The concentrations of the active compounds (alkamides) in the administered products have been in the low mg range per dose. Due to the expected necessary detection of ng ranges, a sensitive and selective LC-ESI-MS-based method that is capable of monitoring plasma levels of traces of active constituents in humans was developed and validated. The resulting maximum concentrations (mean +/- standard deviation) of dodeca-2 E,4 E,8 Z, 10 E/ Z-tetraenoic acid isobutylamides in plasma were 0.22 +/- 0.07 ng/mL after administration of Echinaforce tablets, 0.22 +/- 0.15 ng/mL after taking Echinaforce Junior tablets and 0.23 +/- 0.16 ng/mL after administration of an Echinacea sore throat spray. The areas under the curve were 0.22 ng/mL x h, 0.20 ng/mL x h and 0.23 ng/mL x h, respectively.