Biliary epithelial cells are a primary site of damage in liver allograft rejection and in immunologically mediated diseases such as primary biliary cirrhosis. Human leukocyte antigens and adhesion molecules on the biliary epithelium are associated with T-lymphocytic binding, recognition and destruction. To investigate relevant cellular immunological mechanisms under standard conditions, we have established an in vitro model using human gallbladder epithelial cells. Although not directly affected in these aberrations, gallbladder epithelial cells are excellent objects for immunological investigations. More than 108 highly purified cells were isolated and cultured longer than 6 wk in confluent monolayers. Cell growth was routinely established on uncoated plastic culture dishes, and serum-free media could be applied for immunological experiments. Cell characterization was performed by means of specific monoclonal antibodies typical for biliary epithelial cells. Cytokeratins 1 through 8, 18 and 19 and human epithelial cell antibody 125 always showed strong positive staining. Antigen patterns were examined before and after treatment with interferon-γ by use of immunohistochemical staining methods. Untreated human gallbladder epithelial cells expressed human leukocyte class I antigens but few or no class II antigens. After stimulation with interferon-γ induction of human leukocyte antigen-DR, -DP and -DQ was detected. In addition, intercellular adhesion molecule 1 was induced on these gallbladder epithelial cells. Therefore an immunological competence similar to that of biliary epithelial cells could be demonstrated. In vitro cell cultures of gallbladder epithelial cells offer a promising tool for subsequent investigations concerning intrahepatic biliary epithelial cells and their interactions with cells of the immune system. (HEPATOLOGY 1993;18:546–555.)