Gemcitabine is a first line agent for pancreatic cancer, but yields minimal survival benefit. This study evaluated in vitro and in vivo effects of a monoclonal antibody (TRA-8) to human death receptor 5, combined with gemcitabine, using two human pancreatic cancer cell lines, S2VP10 and MIA PaCa-2. A subcutaneous model of pancreatic cancer was employed to test in vivo efficacy. S2VP10 and MIA PaCa-2 cells were treated with varying doses of gemcitabine and TRA-8. Cell viability and apoptosis were determined with an adenosine triphosphate assay and annexin V staining, respectively. Mitochondrial membrane destabilization was evaluated with fluorescence-activated cell sorting analysis of JC-1 stained cells. Caspase activation was evaluated by Western blot analysis. MIA PaCa-2 subcutaneous xenografts in athymic nude mice were evaluated for response to treatment with 200 μg of TRA-8 (intraperitoneal on days 9, 13, 16, 20, 23, and 27 postimplant) and 120 mg/kg gemcitabine (I.P. on days 10, 17, and 24). Tumor growth was measured with calipers. MIA PaCa-2 and S2VP10 cells receiving combination treatment with TRA-8 and gemcitabine demonstrated enhanced cytotoxicity, annexin V staining, and mitochondrial destabilization compared to either agent alone. Combination treatment produced enhanced caspase-3 and -8 activation in both cell lines compared with either agent alone. In vivo studies demonstrated mean subcutaneous tumor surface area (produce of two largest diameters) doubling times of 38 days untreated, 32 days gemcitabine, 49 days TRA-8, and 64 days combination treatment. TRA-8 is an apoptosis-inducing agonistic monoclonal antibody that produced synergistic cytotoxicity in combination with gemcitabine in vitro through enhanced caspase activation. These findings, with substantial inhibition of tumor growth in a mouse pancreatic cancer xenograft model receiving combination therapy, are encouraging for anti-death receptor therapy in the treatment of pancreatic cancer. © 2006 The Society for Surgery of the Alimentary Tract.