Possible humoral and neural components mediating intracisternal bombesin (500 ng)-induced inhibition of gastric secretion were studied in rats. Intracisternal bombesin induced a marked rise in gastric pH from 2.0 +/- 0.5 up to 6.5 +/- 0.6 whereas gastric secretion in parabiotic saline-treated partners was not modified. Bombesin inhibited pentagastrin-stimulated gastric acid output by 88 +/- 5% in intact rats and 71 +/- 7% in vagotomized animals. Spinal cord transection at the level of the 5th or 7th cervical but not the 8th or 13th thoracic vertebrae significantly reversed the rise in pH and the decrease in acid concentration induced by bombesin and abolished the hyperglycemic effect of the peptide. These results suggest that bombesin inhibitory action on gastric secretion is not mediated through humoral factors but through neural pathways in part related to the sympathetic nervous system along the spinal cord, whereas the parasympathetic outflow from the vagus or the sacral spinal nerves does not seem to play an important role.