Serial serum amylase determinations were made in 85 consecutive patients who presented with an initially elevated value. In 35 patients (Group A), the clinical findings were consistent with biliary tract disease. All underwent cholecystectomy for documented cholelithiasis within a week of diagnosis, and 23 percent had choledocholithiasis as well. Fifty patients (Group B) presented with a first episode of acute alcoholic pancreatitis. An amylase profile, consisting of initial and final values and the daily rate of change, was significantly different between the two groups. The initial serum amylase value was higher in Group A patients and decreased more rapidly to a lower value than in Group B patients. We conclude that both the initial value and pattern of serum amylase decay distinguish the hyperamylasemia of biliary tract disease from that of alcoholic pancreatitis.