AbstractAdministration ofEscherichia coliendotoxin abolished the acid secretory response induced by a bolus injection of pentagastrin in the continuously perfused stomach of the anaesthetized rat. Likewise, acid secretion stimulated by the continuous intravenous perfusion of pentagastrin was inhibited by administration of interleukin‐1β (IL‐1β). In both cases pretreatment withNg‐nitro‐l‐arginine methyl ester (l‐Name) but not dexamethasone or indomethacin substantially restored the secretory responses to pentagastrin. The actions ofl‐Name were reversed by the prior administration ofl‐arginine but not by its enantiomer d‐arginine. Even thoughl‐Name increased blood pressure, this does not seem to be the mechanism by which endotoxin‐induced acid inhibition was prevented, since similar systemic pressor responses induced by phenylephrine had no such effect. The secretory response elicited by pentagastrin in the isolated lumen perfused stomach of the rat was not influenced by incubation (100 min) with IL‐1β. These observations suggest that the acute inhibition of acid responses to pentagastrin by endotoxin and IL‐1β involves nitric oxide