A novel tissue-specific cDNA, PDIp, was previously isolated from human pancreas. It encodes a protein that is structurally and functionally related to protein disulfide isomerase (PDI). To compare the expression pattern of PDI and PDIp in human pancreas and liver tissues, we prepared rabbit polyclonal antiserum against a recombinant glutathione-S-transferase-coupled PDIp fusion protein. Western blot analysis revealed that pancreas expresses both PDI and PDIp, whereas liver only expresses PDI. Rabbit antiserum raised against recombinant PDIp immunostained specifically to the acinar cells of human pancreas. Treatment of PDIp with peptide:N-glycosidase F caused PDIp down shift in the NaDodSO₄-PAGE gel, indicating that PDIp is a glycoprotein. A 2.0-kb message was detected from mouse pancreas using a human PDIp cDNA probe. Similarly, PDIp glycoprotein was detected in mouse pancreas extract by anti-human PDIp antiserum, suggesting that PDIp is highly conserved in human and mouse pancreas. From these studies, we conclude that the pancreas expresses two members of PDI and that PDIp is a glycoprotein specifically expressed in pancreatic acinar cells.