AbstractThe inhibition of acetylcholine‐mediated contraction of guinea‐pig ileum by several phyllanthimide analogues was evaluated.It was observed that maleimide derivatives exhibited high antispasmodic activity, being about 5–8‐fold more potent than the succinimide derivatives, indicating that the double‐bond in the imido ring seems to be important for activity. The distance between the aromatic and the imido ring is also a factor related to the activity; compounds separated into two methylene groups are the most potent. Moreover, the difference in nitrogenated bases in the succinimide derivatives does not significantly affect their antispasmodic a