Dose-response studies were performed in 6 human volunteer subjects to determine the threshold and optimal doses of intravenous bombesin for stimulation of gastric acid secretion and gastrin release. A significant stimulation of both acid and gastrin was obtained with a very low dose, 3 pmol x kg-1 x h-1. Peak stimulation of acid secretion (67% of pentagastrin PAO) was obtained at 12.5 pmol x kg-1 x h-1. Serum gastrin response to this dose of bombesin was similar to that obtained after a high protein meal. Higher doses of bombesin caused further increases in serum gastrin but not in acid secretion. Since very low doses of bombesin, too small to produce detectable increases in immunoreactive serum bombesin, caused parallel increases in gastrin and acid secretion, it is possible that the bombesin-like peptides present in human gastrointestinal tissues contribute to regulation of human gastric secretion.