The effects of intravenous infusions of morphine, met-enkephalin and leu-enkephalin on gastric acid secretion, gastrin release and gastric emptying were investigated in four dogs with gastric cannulas stimulated by a liquid peptone meal. The actions of a potent opiate antagonist, naloxone, used alone or combined with opiates were also studied. Morphine, met-and leu-enkephalin decreased the fractional gastric emptying rate. Acid secretion was decreased by enkephalins and increased by high doses of morphine. Enkephalins and to a lesser degree morphine inhibited gastrin release during the first hour following the administration of the meal. Only leu-enkephalin decreases significantly the integrated gastrin response. Naloxone at the doses used antagonized partly or totally the effects of opiates on gastric emptying but not those on gastric secretion or gastrin release. Naloxone infused alone had no significant effect on the gastric functions tested. These studies indicate that in dogs stimulated by a liquid test meal, enkephalins inhibit gastric emptying, acid secretion and gastrin release. Morphine inhibits gastric emptying and gastrin release and enhances acid secretion.