Infusion of 0.1M ammonium bicarbonate buffer solution into the pancreatic duct in dogs with and without obstruction of the pancreatic veins or portal vein and with or without obstruction or collection of lymph from the thoracic duct revealed that, in the normal canine pancreas, ductal pressures above 40 cm resulted in passage of fluid into the interstitium of the gland. Large volumes of innocuous fluid, such as ammonium bicarbonate buffer, were absorbed by the pancreatic microcirculation, which appears to have extensive collateral outflow pathways. The portal venous bed appeared to be a major route for absorption of fluid from the pancreatic interstitium, while the lymphatic system played a secondary role, and increased in importance when flow in the venous outflow was compromised.