Transcatheter arterial embolization (TAE) has been widely used for treatment of hepatocellular carcinoma. Acute pancreatitis occasionally occurs as a complication of TAE. We have investigated the possible effects of TAE on the pancreas by monitoring serum pancreatic enzyme activities following TAE with various embolic materials. Serum amylase activity was increased very little in the patients treated with chemotherapy alone or plus TAE with lipiodol, slightly increased in many of the patients treated with chemotherapy plus TAE with gelatin sponge, and increased in all of the patients treated with chemotherapy plus TAE with gelfoam powder. The activity was increased to a level as high as 700 U/dl or more in most individuals of the last category. In one of them acute pancreatitis developed, probably because the gelfoam powder regurgitated into the pancreaticoduodenal artery, and occluded a very peripheral portion of the pancreatic vascular bed, leading to ischemia of the pancreas. These results suggest that choosing the correct particle size is important for prevention of acute pancreatitis.