When using clinical criteria, both falsely positive and falsely negative diagnoses of acute pancreatitis (AP) are often made. Based on a clinical study, elevated serum levels of the pancreatic lipolytic enzyme carboxylic ester hydrolase (CEH) was recently suggested to be a highly specific marker of acute pancreatitis. To determine the sensitivity of the test for AP, a study on patients with the diagnosis set objectively was necessary. In the present study, AP was diagnosed by contrast-enhanced computed tomography in 64 patients, and histopathological examination of tissue removed at laparotomy in 18 of them. By these criteria, 42 patients suffered from acute interstitial pancreatitis (AIP), and 22 patients from necrotizing pancreatitis (NP). Based on the CEH concentrations in the first serum sample obtained in each patient, the sensitivity of CEH for pancreatitis was 98%. From the second day after admission, CEH levels in patients with NP were significantly higher than in patients with AIP. Furthermore, in patients with NP, CEH values remained at a raised level for the following 10 d, whereas a significant decrease of CEH values was noted in patients with AIP. In contrast, total serum amylase activities were higher in patients suffering of AIP than in patients suffering of NP during the observation period. We conclude, that the sensitivity of the CEH test is very high for AP. CEH concentrations remaining at a high level are suggestive of NP, whereas diminishing CEH levels are suggestive of AIP.