After pancreas transplantation, signs of acute pancreatitis are found in the grafted tissue. Pancreatic juice secreted from this organ was analyzed by gel electrophoresis. Initially, the pattern of secretory proteins was similar to that of the juice collected from normal individuals, but high levels of albumin were present. Within 2 days after reperfusion of the grafted pancreas, proteins of molecular weights 17,000-20,000 increased remarkably. Separation by two-dimensional gel electrophoresis showed that this was largely due to the appearance of new a protein, present neither in the juice collected immediately after reperfusion nor in normal pancreatic juice. After transfer onto nitrocellulose, this additional protein was detected by antibodies directed against the recently described rat "pancreatitis-associated protein." Maximal amounts of approximately 7.5% of total secretory protein were found 5 days after transplantation. The concentration of the protein decreased in the further course but was still detectable after 45 days. The isoelectric point (7.1) and the molecular weight (17,500) were similar to those of the rat protein. It is concluded that after inflammation induced by pancreatic transplantation, the human pancreas secretes high amounts of a protein not present in normal juice. Because of its similarities to the rat pancreatitis-associated protein it is designated human pancreatitis-associated protein.