Résumé : High concentrations of antiinflammatory steroids (2.5-40 μg/ml) reversibly inhibited the electrically induced contractions of the guinea-pig isolated ileum. At 40 μg/ml they also reversibly inhibited contractions clicited by acetylcholine, histamine, nicotine and 5-hydroxytryptamine. PGE1 (2.5 ng/ml), PGE2 (2.5 ng/ml) and PGF2α (25 ng/ml) antagonized these effects. The inhibition of contractions elicited by direct agonists were less pronounced than those elicited by indirect or partly indirect agonists. The inhibitory effect of steroids may be related to non-specific actions on biological membranes. An overall sensitization of the smooth muscle by PG's may explain their antagonism to inhibition by steroids. © 1979 Springer-Verlag.