When pancreatic juice which was collected separate from bile was diverted from the duodenum of rats for 24 hr, the basal flow rate of juice and its output of protein increased greatly over values recorded immediately after operation. Similar increases were recorded when pancreatic juice was recirculated back into the duodenum for 24 hr. Infusion of bicarbonate or enzyme into the duodenum failed to affect these increases in secretion. Thus the hypersecretion of juice did not appear to be the result of loss of juice from the duodenum. Attempts were then made to estimate rates of pancreatic secretion without diverting bile from the common bile duct. Immediately after operation, rates of pancreatic secretion estimated indirectly from the differences between combined bile‐pancreatic juice and bile alone were higher than in those rats in which pancreatic juice was collected by diverting bile from the common bile duct. This suggested that bile in some way assisted the passage of viscous pancreatic juice down the common bile duct. Indirect estimates of pancreatic secretion made 24 hr after operation were greater than the estimates made immediately after operation but were similar to those values obtained after 24 hr in rats from which pure pancreatic juice was collected. This was taken as evidence to support the view that the trauma associated with anaesthesia and surgery may depress the rate of pancreatic secretion and that hypersecretion of juice may indeed be a normal phenomenon. In contrast to the situation reported to exist in dogs, indirect estimates of the effects of feeding on pancreatic secretion were similar irrespective of whether secretions were diverted from or returned to the duodenum.