We studied the effect of raw soya flour (RSF) given as a single gavage or for long-term periods on pancreatic blood flow. These effects were compared with the response to treatment with cholecystokinin (CCK) since it has been suggested that RSF feeding releases CCK. In acute experiments total pancreatic blood flow was significantly increased after infusion of CCK (60 Ivy dog units X kg-1 X h-1) and after gavage with preparations of RSF or heated soya flour (HSF). When expressed as flow per 100 g pancreatic weight, the greatest increase was seen after gavage with RSF. In separate chronic studies, total pancreatic blood flow was significantly increased in rats fed RSF for 4 wk compared with rats fed HSF, but because of pancreatic enlargement in rats fed RSF flow per 100 g pancreatic weight was similar in the two groups. When rats fed RSF for 4 wk were changed to standard rat cubes for 48 h before study, pancreatic blood flow (ml/min and ml X min-1 X 100 g pancreas-1) and total pancreatic DNA decreased significantly compared with rats fed RSF continuously. However, when CCK was infused intravenously during the 48-h period on cubes, pancreatic blood flow and DNA remained significantly increased and were not significantly different from values in rats fed RSF continuously. These results show that the effects of RSF feeding and CCK treatment on pancreatic growth and blood flow are similar and are consistent with the postulated role of CCK as the trophic hormone released by RSF feeding.