Abstract Sodium ricinoleate, dioctyl sodium sulfosuccinate, sodium dodecyl (lauryl) sulfate, polysorbate 80, sodium deoxycholate and chenodeoxycholate were found to produce depression of in vitro mucosal and smooth muscle cell function. These actions were assessed by measuring net water and electrolyte transport from everted hamster gut sacs and contractile activity of the electrically stimulated guinea-pig ileum. All compounds were effective depressants of both systems at concentrations which were likely to be below their respective critical micellar concentration. Ricinoleic acid may produce its cathartic effect due to its amphipathic nature, possibly by hydrophobic interaction with membrane lipoproteins. Ricinoleic acid and the other surfactants may be acting through a common mechanism.