The serum behavior of amylase, pancreatic isoamylase, lipase, trypsinogen, and elastase 1 was studied in 145 patients with pancreatic disease and in 66 patients with abdominal pain of nonpancreatic origin, for the purpose of evaluating the relative diagnostic utility of their assays. In 34 patients with acute pancreatitis, serum lipase, trypsinogen, and elastase 1 were elevated in all 34, pancreatic isoamylase in 33 (97%) and amylase in 30 (88%). Ten of these acute pancreatitis patients were followed sequentially for seven days: the variations in their serum enzyme levels were parallel, although the lipase, trypsinogen, and particularly the elastase 1 elevations persisted longer than did those of amylase and pancreatic isoamylase. Among the patients with chronic pancreatitis, either in painful relapse (N = 19) or with pancreatic cysts (N = 15), the respective percentages of enzymes elevations were: 79 and 80% for elastase 1, 68 and 67% for trypsinogen, 63 and 73% for pancreatic isoamylase, 58 and 60% for lipase, 53 and 60% for amylase. In the 52 chronic pancreatitis patients studied during clinical remission, serum enzyme behavior varied greatly, and a majority of the assays (60%) were normal; even in the case of severe pancreatic exocrine insufficiency, normal as well as abnormally high and low enzyme values were seen. Highly variable enzyme behavior was also seen in the 40 patients with pancreatic cancer, and elastase I was the most frequently (35%) elevated enzyme in this group as well. Among the patients with abdominal pain of nonpancreatic origin, abnormally high enzyme levels were present in percentages ranging from 6% for lipase to 21% for trypsinogen.(ABSTRACT TRUNCATED AT 250 WORDS)