The release of pancreatic polypeptide (PP) by gut hormones, acetyl choline and adrenaline was investigated in an isolated perfused pancreas preparation. PP was potently released by 1 nmol/1 caerulein (186 +/- 12%, p is less than 0.001) and gastric inhibitory peptide (GIP) (211 +/- 31%, p is less than 0.005) as well as by 1 mumol/1 acetyl choline (1097 +/- 59%, p is less than 0.001). A significant two-fold release of PP was also evoked by 1 nmol/1 vasoactive intestinal peptide (VIP) (129 +/- 38%, p is less than 0.02 and gastrin (108 +/- 25% p is less than 0.01). Insulin release, induced by high glucose concentration was enhanced by both GIP (210 +/- 38%, p is less than (0.01) and VIP (48 +/- 5%, p is less than 0.001). In addition GIP enhanced the release of glucagon by 179 +/- 18% (p is less 0.001) at 1.4 mmol/1 glucose and by 127 +/- 24% (p is less than 0.005) at 8.3 mmol/1 glucose. Thus no simple inter-relationship appears to exist between the control of the three circulating islet hormones.