Abstract The effects of 1-h infusions of bombesin and gastrin releasing peptide (GRP) at 50 pmol/kg per h and neurotensin at 100 pmol/kg per h on gastrin, pancreatic polypeptide (PP) and neurotensin release in man were determined following either saline or atropine infusion (20 μg/kg). Bombesin produced a rise in plasma neurotensin from 32 ± 6 to 61 ± 19 pmol/l and of PP from 26 ± 8 to 36 ± 7 pmol/l. There was a further rise of plasma PP to 50 ± 13 pmol/l after cessation of the infusion. GRP had no significant effect on plasma neurotensin, but compared to bombesin, produced a significantly greater rise in plasma PP from 34 ± 6 to 66 ± 19 pmol/l during infusion. There was no post-infusional increase. At this dose, GRP was as effective as bombesin in releasing gastrin, although unlike bombesin its effect was enhanced by atropine. Neurotensin produced a rise in plasma PP from 17 ± 4 to 38 ± 8 pmol/l. Atropine blocked the release of PP during GRP and neurotensin infusion. Atropine had no effect on neurotensin or PP release during bombesin infusion, but did block the rise in plasma PP following bombesin infusion. We conclude that, in contrast to meal-stimulated neurotensin release, bombesin-stimulated neurotensin release is cholinergic independent. Despite structural homology, bombesin and GRP at the dose used are dissimilar in man in their actions and sensitivity to cholinergic blockade.