The most commonly used serum enzymes in pancreatic diseases are total amylase, pancreatic isoamylase, lipase and trypsin. To determine which of these enzymes is the most useful in the diagnosis of clinically quiescent chronic pancreatitis and which enzyme best reflects exocrine functional reserve, we studied 22 healthy control subjects, 44 patients with gastrointestinal, liver and biliary tract diseases, and 25 patients with chronic pancreatitis. On the basis of duodenal intubation, the latter were divided into two subgroups: one group of 13 patients with slight to moderate secretion deficiency and another of 12 patients with severe exocrine insufficiency. Of the enzymes studied, lipase, trypsin and pancreatic isoamylase are equally suitable for the evaluation of function in severe chronic pancreatitis, but not for the early diagnosis of the disease. Results for total amylase are not reliable so that its use in the study of chronic pancreatitis is not advisable.