1 The role of cannabinoid (CB) receptors in the regulation of gastric acid secretion was investigated in the rat by means of functional experiments and by immunohistochemistry. 2 In anaesthetized rats with lumen-perfused stomach, the non selective CB-receptor agonist WIN 55,212-2 (0.30 ± 4.00 mmol kg 71 , i.v.) and the selective CB 1 -receptor agonist HU-210 (0.03 ± 1.50 mmol kg 71 , i.v.), dose-dependently decreased the acid secretion induced by both pentagastrin (30 nmol kg 71 h 71 ) and 2-deoxy-D-glucose (1.25 mmol kg 71 , i.v.). By contrast, neither WIN 55,212-2 (1 ± 4 mmol kg 71 , i.v.) nor HU-210 (0.03 ± 1.50 mmol kg 71 , i.v.) did modify histamine-induced acid secretion (20 mmol kg 71 h 71 ). The selective CB 2 -receptor agonist JWH-015 (3 ± 10 mmol kg 71 , i.v.) was ine ective. 3 The gastric antisecretory e ects of WIN 55,212-2 and HU-210 on pentagastrin-induced acid secretion were prevented by the selective CB 1 -receptor antagonist SR141716A (0.65 mmol kg 71 , i.v.) and una ected by the selective CB 2 -receptor antagonist SR144528 (0.65 ± 2 mmol kg 71 , i.v.). 4 Bilateral cervical vagotomy and ganglionic blockade with hexamethonium (10 mg kg 71 , i.v., followed by continuous infusion of 10 mg kg 71 h 71 ) signi®cantly reduced, but not abolished, the maximal inhibitory e ect of HU-210 (0.3 mmol kg 71 , i.v.) on pentagastrin-induced acid secretion; by contrast, pretreatment with atropine (1 mg kg 71 , i.v.) did not modify the antisecretory e ect of HU-210. 5 Immunoreactivity to the CB 1 receptor was co-localized with that of the cholinergic marker choline acetyltransferase in neural elements innervating smooth muscle, mucosa and submucosal blood vessels of rat stomach fundus, corpus and antrum. In contrast, CB 2 receptor-like immunoreactivity was not observed. 6 These results indicate that gastric antisecretory e ects of cannabinoids in the rat are mediated by suppression of vagal drive to the stomach through activation of CB 1 receptors, located on pre-and postganglionic cholinergic pathways. However, the ine ectiveness of atropine in reducing the e ect of HU-210 suggests that the release of non cholinergic excitatory neurotransmitters may be regulated by CB 1 receptors.