Exocrine pancreatic secretion to intravenous injections of a new stimulant of gastrointestinal motility, R51,619 (cisapride) was studied in conscious rats, and in the isolated pancreatic acini in vitro. The injection of cisapride (2 mg/kg) significantly increased fluid, bicarbonate and protein output in vivo. Atropine completely abolished the pancreatic responses to cisapride, and CR 1409, a new glutaramic acid derivative and a competitive cholecystokinin (CCK) inhibitor, tended to decrease the cisapride-induced pancreatic exocrine secretion. However, amylase release and Ca2+ efflux from the isolated pancreatic acini were not stimulated. These results suggest that cisapride indirectly affects the pancreatic exocrine secretion primarily by releasing acethycholine from the intrapancreatic nerve endings and in part by releasing CCK from the duodenum, but has no direct action on the pancreas.