We compared results of measurements of total serum amylase, pancreatic isoamylase, and lipase measurements in patients with hyperamylasemia. Serial measurements of these three enzyme levels in patients recovering from acute pancreatitis indicated that pancreatic isoamylase and lipase were elevated above normal to a greater extent and remained elevated much longer than did the total amylase. This finding indicates an appreciable sensitivity advantage of the pancreatic isoamylase and lipase over total amylase measurement during the recovery phase of pancreatitis. Comparison of pancreatic isoamylase and lipase levels in selected sera indicated a good correlation (r = 0.84) between these two measurements in patients who did not have macroamylasemia. Lipase was normal in sera with amylase elevations due solely to salivary isoamylase. Thus, in nonmacroamylsemic sera, pancreatic isoamylase and lipase appear to be roughly interchangeable markers of the level of pancreatic enzymes in the blood. An advantage of the lipase assay is that this enzyme is normal in hyperamylasemia caused by macroamylasemia, whereas the inhibitor assay indicates that the pancreatic isoamylase is elevated. Development of automated assays for either pancreatic isoamylase or lipase should lead to the routine use of one of these assays in place of the present reliance on total amylase measurements in the diagnosis of pancreatitis.