Objectives:The aim of the present study was to evaluate the changes caused by intravenous administration of regulatory peptides, bombesin (BBS) and neurotensin (NT), on gastric secretion, serum gastrin, and plasma levels of bombesin-1ike immunoreactivity (BLI) and neurotensin. Materials and methods: Fourteen dogs underwent an upper gastrointestinal tract operation and a Pavlov pouch for the concentration of gastric fluids was formed. The experimental animals were divided into two groups. Peptides were given one month after the second operation and after fasting for 12 hours. In group A, the effects of BBS were studied after a rapid 1 ìg/kg body weight dose and a slow 30´ 0.5 ìg/kg body weight dose administration intravenously. Correspondingly to group B the effects of NT were studied in the same way. Results:The rapid intravenous infusion of BBS caused a very significant increase in gastrin levels, BLI in plasma, volume and HCl of the gastric fluids. The same results, plus a significant decrease in gastric pH, were observed following slow intravenous infusion of BBS. Concerning the NT, rapid administration caused a significant decrease in the volume of gastric fluids. Slow NT administration of caused a significant reduction in gastric fluid volume and in HCl. On the contrary, pH was significantly increased. Conclusion:Bombesin increases plasma gastrin levels and HCl secretion. Neurotensin administration causes a decrease in HCl secretion without affecting gastrin levels in plasma.