The factors causing a decline in renal perfusion were studied in anaesthetized dogs with acute pancreatitis 4 h after the forceful injection of bile into the pancreatic duct. In 11 such dogs, glomerular filtration rate (GFR) decreased by 40.4% from the control state (P less than 0.05), whereas the clearance of para-aminohippurate (CPAH) declined by 50.2%. These changes were associated with a 15.3% decline in cardiac output (P less than 0.05) and a 26.2% fall in plasma volume. Glomerular morphology was entirely normal. When hypovolemia was prevented by infusing homologous plasma over the 4-h period of observation, the normally observed decline in GFR, CPAH, and cardiac output was prevented. The decline in plasma volume, associated with a rising hematocrit and declining plasma protein concentration, and the associated decrement in renal perfusion, could be entirely duplicated by the infusion of trypsin, chymotrypsin, elastase, and phospholipase A2 (but not lipase or amylase) into normal dogs. These perturbations also were prevented by the concurrent infusion of 4% albumin in saline. At 24 h, however, the renal failure became unresponsive to volume replenishment. We conclude that the decline in renal perfusion in dogs at 4 h with acute pancreatitis is entirely due to hypovolemia, induced by the release of specific enzymes from the inflamed gland, which causes the loss of protein-rich plasma from the vascular space.