Fifty-five leukocyte scintigraphies were performed. Thirty-five patients (group 1) with acute pancreatitis in the early phase and 20 patients (group 2) with pancreatic chronic pseudocysts following acute pancreatitis were tested. The clinical features, laboratory parameters, and Ranson classifications were registered during hospitalization. In group 1, most of the cases with a severe clinical outcome gave positive leukocyte scintigraphic results (10/12). Leukocyte accumulation was also detected in patients with mild acute pancreatitis (4/23), but at a lower frequency. In the acute phase, significant differences in laboratory parameters (sedimentation rate and leukocyte count) were found in the leukocyte scintigraphy-positive versus -negative cases. The scintigraphic activity correlated with the sedimentation rate, leukocyte count, fever, and duration of hospitalization. In group 2 there were five cases with a positive leukocyte scan. A pancreatic abscess was found in four of them during surgery. In seven patients with a normal scintigram, surgery revealed a noninfected pancreatic pseudocyst. Leukocyte infiltration of the pancreas can be demonstrated by leukocyte scintigraphy. A positive leukocyte scan indicated a severe course of acute pancreatitis. The method also seems useful for differentiation between infected and noninfected chronic pancreatic pseudocysts.