BACKGROUND Acute pancreatitis with high mortality of severe onset is still a major problem in medicine. Early identification of the severity of the disease is critical for effective treatment. Many markers have been tried and are still being tested. The ideal marker should be able to identify the cases and distinguish between mild and severe. METHODS This prospective study included 34 cases (14 males, 20 females, mean age: 58 years) of acute pancreatitis and 33 cases (17 males, 16 females, mean age: 53 years) as a control group. Mild (n=29) and severe (n=5) cases were compared with respect to serum levels of amylase, C-reactive protein (CRP), alpha-1-protease inhibitor, and antichymotrypsin on admission and 24 and 48 hours (h) after admission. RESULTS Alpha-1 protease inhibitor and antichymotrypsin levels were significantly elevated in the first 24 h; however, CRP peaked after 48 h in the acute pancreatitis group. While CRP showed significantly higher concentrations in patients with severe pancreatitis, alpha-1-protease inhibitor and antichymotrypsin levels changed slightly, but without significance, in severe cases. CONCLUSIONS Alpha-1 protease inhibitor and antichymotrypsin are early events in acute pancreatitis, with high levels on admission. Activation of these variables declines after 24 h. These markers may have early diagnostic value in patients with acute pancreatitis. Because neither of them is good at discrimination of mild and severe cases in the disease, they should not be incorporated into routine clinical investigations.