In the present study, the effects of acute p.o. administration of placebo at 300 mg and 600 mg of WS 5570 Hypericum perforatum extract on cortisol (COR), growth hormone (GH) and prolactin (PRL) secretion were examined in twelve physically and mentally healthy subjects. WS 5570 is a hyperforin containing extract of St. John's Wort which has been proven effective in mild to moderate depression. After inserting an i.v. catheter, blood samples were drawn one hour prior to the administration of WS 5570 or placebo, at the time of application and up to five hours after application in 30-minute intervals. Plasma concentrations of COR, GH, and PRL were determined in each blood sample by double-antibody RIA methods. No PRL stimulation could be observed after placebo or after WS 5570 (300, 600 mg). A small but statistically significant elevation in GH AUC values occurred after 300 mg of WS 5570. After 600 mg of WS 5570, a clear-cut COR stimulation was observed, occurring from 30 up to 90 minutes after the application. In this period of time (from t = 30 min to t = 90 min), the mean COR concentrations were significantly higher after 600 mg of WS 5570 compared to placebo. 300 mg of WS 5570 did not show any effects on COR secretion. We propose that the Hypericum extract WS 5570 is able to influence central neurotransmitters, thereby causing COR stimulation in a dose-dependent manner.