Macroamylasemia is a recently described condition of unknown cause characterized by elevated serum amylase concentrations without hyperamylasuria. No particular clinical signs or symptoms accompany this finding. However, postoperative determinations of serum amylase in such patients may occasion great alarm, since the hyperamylasemia may be confused with that due to pancreatitis, perforated or ischemic bowel, or other serious condition. The simple practice of determining urinary amylase values at the same time as serum amylase will provide the major clue for diagnosis. A new method for rapid detection of the macroamylase complex found in this syndrome provides a definitive capability for separating patients with macroamylasemia from those with pathologic causes for the elevation of serum amylase.