Animal experiments were performed to compare several types of contrast materials using conditions which simulate those employed in reflux pancreatography. The water soluble agent, sodium diatrizoate, was markedly superior to barium and oily contrast agents. It was observed that sodium diatrizoate passes through the pancreas rapidly and that a pyelogram results. It is postulated that a ductovenous pathway is utilized keeping contact of the water soluble contrast material with acinar cells to a minimum while allowing sufficient pancreatic opacification for diagnostic study. Reflux pancreatography with sodium diatrizoate can be advocated in humans on the basis of safety in animal experiments.