Pancreas of normal dogs and the inflamed gland of experimental pancreatitis were studied by intra-arterial injection of Microfil, a silicone-rubber compound especially suited for study of the microcirculation. Duodenal vasculature and lobular vessels of the pancreas were studied as were those supplying the duct. Inter-lobular vessels were well visualized in the normal pancreas and intralobular vessels formed a fine reticular pattern throughout the cleared lobules. A complex network of vessels in the pancreatic duct was observed using this technique, apparently derived from the interlobular vessels. The blood supply of each layer of the duodenum was evaluated. Intraductal trypsin injection produced focal areas of pancreatitis associated with edema, poor vascular filling and spastic changes of the lobular vessels. Extravasation of Microfil, although not apparent on normal specimens, was prominent in inflamed specimens and suggested vascular weakness and disruption. Pancreatic lobules adjacent to inflammatory areas showed definite evidence of dilatation. The inflamed pancreatic ducts were markedly edematous, thickned, and showed incomplete vascular filling. When the duodenum adjacent to pancreatitis was injected with Microfil, edema and vasoconstriction were especially prominent in the duodenal muscular layer.