The influence of intraluminal infusions of saline and a pancreatic juice-bile salt mixture on transit was determined in bypassed segments of intestine in rats. Animals underwent bypass of 70% of their jejunoileum and insertion of a catheter into the proximal end of the bypassed segment. After recovery from operation, each animal was placed into a harness that allowed free movement while fluids could be infused into the bypassed segment. Beginning on the first postoperative day, the bypassed loops were infused with either saline or a pancreatic juice-bile salt mixture. Transit in these animals was determined on the third day after operation. Other animals received no infusions and were tested either on the third or the 35th day after operation. Animals that received no infusions had low rates of transit when tested either in the fasted or fed condition three days after operation. Saline infusions resulted in a slight increase in transit in fasted animals only. Transit rates were increased to a greater degree following infusion of the pancreatic juice-bile salt mixture than with saline, especially in fasted animals in whom the rates approached those seen in the uninfused, fasted animals that were tested 35 days after operation. These findings are consistent with the hypothesis that the reduced transit seen in the bypassed loops of rats three days after operation may be due to intestinal contents characterized by deficiencies in pancreatic juice and bile salts.