The intraduodenal application of a potent protease inhibitor (camostate, 600 mg) causes a significant increase in basal pancreatic secretion in the manner of a negative-feedback mechanism. The integrated protein secretion during the entire study period was 9.9 +/- 1.8 g in 120 min. The iv application of anti-GRP immunoglobulin caused a significant reduction to 5.0 +/- g in 120 min. No significant changes in the plasma concentrations of GRP and CCK were detectable. The increased secretion occurring after the administration of the protease inhibitor could be mediated by neural GRP-dependent mechanisms. These may also be relevant for CCK-dependent factors, which are only briefly mentioned.