The fact that esterolytic activity is significantly elevated in plasma of patients with acute pancreatitis and that it correlates with the serum amylase level was confirmed. No kinin activity, however, was detected in plasma. To characterize the esterolytic activity, patient and normal plasmas were chromatographed on Sephadex G-200 and the esterolytic and the kinin-forming activities of each fraction were examined. In the present study, it was speculated that during attacks of acute pancreatitis, kallikrein with amylase might be liberated into blood from the pancreas. It was confirmed that almost all of the kallikrein liberated was combined with alpha1-macroglobulin, and alpha2-macroglobulin-bound kallikrein itself possessed kinin-forming activity.