Background. The Fas (APO-1/CD95) receptor/Fas ligand (FasR/FasL) system plays a key role in immune surveillance. We investigated the possibility of a tumor escape mechanism involving the FasR/FasL system in pancreatic cancer cells. Methods. Fourteen pancreatic cancer cell lines and 3 pancreatic cancer surgical specimens were studied for their expression of FasR and FasL by flow cytometry, immunoblotting, and immunohistochemistry. FasR function was tested with an anti-FasR antibody. FasL function was assessed by coculture assays using pancreatic cancer cells and FasR-sensitive Jurkat T-cells. Results. FasR was expressed in normal pancreas, in 14 of 14 pancreatic cancer cell lines, and in 3 of 3 surgical specimens. However, only 1 of 14 cancer cell lines expressed functional FasR when grown in monolayer, although 3 additional cell lines displayed functional FasR when cultured in suspension. Normal pancreas did not express FasL, whereas 14 of 14 cancer cell lines and 3 of 3 surgical specimens expressed FasL. FasL expressed by pancreatic cancer cells mediated killing of Jurkat T-cells in coculture assays (P < .005). Conclusions. These data suggest that pancreatic cancer cells have 2 potential mechanisms of evading Fas-mediated immune surveillance. A nonfunctional FasR renders them resistant to Fas-mediated apoptosis. The aberrant expression of functional FasL allows them to 'counterattack' activated Fas-sensitive T- cells. Alone or in unison, these tumor escape mechanisms may contribute to the malignant and often rapid course of pancreatic cancer disease.