Water soluble contrast material infused into the pancreatic duct is followed rapidly by roentgenographic visualization of the urinary tract in the dog. Iodinated contrast materials have been found to exhibit the property of opacity on electron micrographic study so that their location can be established. Biopsy specimens of the pancreas obtained at the time of infusion of contrast material demonstrated opaque material on electron microscopic evaluation. Simultaneous renal biopsies showed similar material in the brush border of the proximal convoluted tubule before it was visible roentgenographically. Evidence is presented to document the pancreatic ducto-interstitial-venous pathway postulated in 1909 by Herring and Simpson.3 The observation that iodine containing roentgenographic contrast agents are visualized with the electron microscope offers wide possibilities for obtaining multiple static views of rapidly evolving physiologic processes.