Exocrine pancreatic secretion in conscious dogs is significantly stimulated by the intravenous application of small doses of gastrin-releasing peptide (GRP; 30 pmol x kg-1 x h-1). There is no increase of the GRP concentrations in peripheral blood which is also the case under physiological postprandial conditions. There is also no increase in the peripheral cholecystokinin (CCK) concentrations, in contrast to previous reports. Nevertheless other CCK-related mechanisms may play an important role, since the administration of the highly specific CCK receptor antagonist MK-329 causes a marked reduction of the GRP-induced exocrine pancreatic secretion.