AbstractEnteric‐coated preparations containing a fixed peppermint oil/caraway oil combination (e.g. Enteroplant®) are widely used in patients with functional dyspepsia. The effect of a separate intraduodenal application of the active ingredients of Enteroplant® (90 mg peppermint oil (WS® 1340), 50 mg caraway oil (WS® 1520) per capsule) and of a hydrophobic phase galenic auxiliary material contained in the Enteroplant® formulation (dose as contained per capsule) on gastroduodenal motility were studied with stationary manometry in healthy volunteers. The carrier demanded by the experimental setup also served as a control. The results showed that: (1) during phase III of the migrating motor complex (MMC) the frequency and duration of contractions showed a significant decrease in the duodenum for WS® 1340; (2) WS® 1520 significantly reduced the contraction amplitudes in the duodenum during phase I and II of the MMC; (3) trends for decreased values were seen for WS® 1340 in the gastric corpus and duodenum and for WS® 1520 in the gastric antrum; (4) in the gastric corpus the duration of contractions was significantly reduced after application of WS® 1340 during phases I and II of the MMC; (5) WS® 1520 significantly reduced the contraction amplitudes and the duration of contractions in the gastric corpus during phase III of the MMC; (6) for the hydrophobic phase a moderate but significant decrease of duration of contractions in the duodenum and of frequency of contractions in the gastric corpus was seen. No adverse events were observed during the study. In conclusion, it could be shown that both WS® 1340 and WS® 1520 contribute to the efficacy of Enteroplant®. They act locally in the stomach and duodenum to produce smooth‐muscle relaxation. The effects of the active ingredients WS® 1340 and WS® 1520 substantially exceed the effects observed with the galenic auxiliary material and the carrier, respectively. Copyright © 2003 John Wiley & Sons, Ltd.