This single-blind placebo-controlled study was designed to investigate the dose-dependent vagolytic and vagotonic effects after a single oral administration of Atropa belladonna tincture (ABT, 0.1 mg/ml alkaloid concentration, atropine/scopolamine = 20:1). In eight healthy young subjects, heart rate and noninvasive arterial finger blood pressure were recorded simultaneously over 4 h after oral application of four different doses of ABT (day 1: 2 ml, day 2: placebo, day 3: 5 ml, day 4: 1 ml). On each day, 14 20-min sequences under controlled experimental conditions were performed. Among others, mean RR interval (RR), high-frequency spectral power of heart rate variability (HF), and noninvasive baroreflex sensitivity (BRS) were calculated during metronome breathing in supine position. These parameters were robust markers of vagal activity. One hour after 5ml ABT, RR, HF and BRS decreased clearly in six of eight subjects. This effect was interpreted as vagolytic response. After 1 and 2 ml ABT, and after placebo, RR and HF increased markedly. The increase after ABT was much higher than the increase solely due to adaptation after placebo administration, and it could be clearly identified as an augmentation of vagal cardiac activity caused by low-dose ABT. In conclusion, low doses of orally administered ABT can be effectively used to stimulate parasympathetic activity in man. The mode of vagal activation changes between 2 and 5 ml ABT from vagotonic to vagolytic. ABT has no or very little effect on blood pressure control.