Atropine inhibits the post-prandial gastrin release after truncal vagotomy in the dog. Whether this action of atropine is due to suppression of stimulatory cholinergic fibres in the sympathetic nerves of the stomach and the upper small intestine or due to blockade of intrinsic gastric cholinergic mechanisms is unknown. Conscious dogs were fed a meat meal (35 g/kg body weight) before and after truncal vagotomy and after truncal vagotomy plus coeliac and superior mesenteric ganglionectomy. Experiments were repeated in the presence of atropine (50 micrograms/kg body weight, given as an i.v. bolus 60 min prior to the meal). In another set of dogs, only ganglionectomy was performed and the same experiments were done as in the first set of dogs. Truncal vagotomy enhanced the post-prandial 120 min integrated plasma gastrin response by 2.6 times as compared to the response with the vagus nerves intact. Before truncal vagotomy, atropine enhanced the integrated plasma gastrin response by 2.6 times; after truncal vagotomy atropine suppressed this response by 2.3 times. After truncal vagotomy, with or without atropine, additional coeliac and superior mesenteric ganglionectomy did not alter the integrated plasma gastrin response. With the vagus nerves intact, ganglionectomy alone had no effect on the integrated plasma gastrin response whether or not atropine was given. The finding that atropine suppresses the post-prandial plasma gastrin response to a meal after truncal vagotomy and coeliac and superior mesenteric ganglionectomy, i.e. cutting the extrinsic nerves of the stomach and the upper small intestine, suggests the existence of stimulatory cholinergic intrinsic fibres located within the stomach.