Synthetic neurotensin (NT) was infused intracerebroventricularly in 14 mongrel dogs to study the effects of the peptide on gastric secretion and on gastrin and NT levels. The infusion was performed with a specific apparatus, and gastric fluid was collected with a Pavlov pouch. NT was given in two series of experiments: as a bolus intracerebroventricular injection of 269.8 pmol/kg and as a continuous intracerebroventricular infusion at a rate of 539.6 pmol/kg/h for 30 min. The bolus injection caused a very significant decrease of gastric fluid volume, a significant decrease of HC1 output and a significant increase of its pH, while serum immunoreactive gastrin increased significantly. The continuous infusion of NT caused similar changes in gastric secretion. The plasma NT levels did not change. In conclusion, the intracerebroventricular administration of NT increases the serum gastrin levels, decreases the volume and HC1 content of gastric fluid, and increases its pH.