The variations of serum levels of amylase, pancreatic isoamylase, lipase, trypsinogen, and elastase 1 were evaluated in 21 patients with acute pancreatitis. The patients were studied for a mean period of 7 consecutive days (range 5-12 days) after admission to the hospital. On the day of onset of acute pancreatitis, all enzyme levels were abnormally high; pancreatic isoamylase showed the greatest increase compared with its upper normal limit, whereas the increase increment for elastase 1 was the lowest. Subsequently, all enzyme levels except elastase 1 decreased in a parallel fashion. On the eighth day of the study only elastase 1 levels were above normal values in all patients examined, while abnormally high values of lipase were found in 85% of the patients, trypsinogen in 58% of the patients, pancreatic isoamylase in 43%, and total amylase in 23%. These results indicate that, for the early diagnosis of acute pancreatitis, the determination of any of these enzymes is equally efficient, but that elastase 1 is the most sensitive marker of acute pancreatic damage in later stages of the disease.