A test used to help find out if secretion of pancreatic polypeptide (a protein released by the pancreas) is normal or caused by a tumor. A drug called atropine sulfate is injected into the patient’s vein and level of pancreatic polypeptide in the blood is measured. If there is a tumor, the injection will not change the level of pancreatic polypeptide. If there is no tumor, the level of pancreatic polypeptide will drop.