Three different molecular forms of cholecystokinin (CCK-39, -33, and -8) were used in concentrations from 10(-11) to 19(-8) mol/l to stimulate the endocrine and exocrine secretion from the isolated perfused porcine pancreas. During perfusion with a glucose concentration of 7.5 mmol/l CCK-39 in the highest concentration increased the insulin secretion slightly. No significant effect was observed at lower glucose concentrations (5.0 and 3.5 mmol/l). CCK-33 and -8 did not stimulate the secretion of insulin significantly, and neither of the cholecystokinins increased the secretion of glucagon and bicarbonate. All three molecular forms stimulated the secretion of fluid and protein in concentrations above 10(-11) mol/l in a dose-dependent manner and with equal potency. We conclude that the effect of these three cholecystokinins on the endocrine pancreas is without physiological significance, whereas all three are sufficiently potent to play a role in the control of pancreatic protein secretion.