Pancreatic cancer has low levels of antioxidant enzymes including manganese superoxide dismutase (MnSOD), which converts superoxide radical (O(2)(*-)) into hydrogen peroxide (H(2)O(2)), and glutathione peroxidase (GPx), which converts H(2)O(2) into water. Recent studies have demonstrated that overexpression of MnSOD has a tumor-suppressive effect in pancreatic cancer. However, GPx overexpression has been shown to reverse the tumor cell growth inhibition caused by MnSOD overexpression in other types of cancer. Our aims were to determine if overexpression of GPx alters in vitro pancreatic cancer cell behavior and if delivering the GPx gene directly to tumor xenografts alters growth and survival. In vitro, AdGPx slowed tumor growth by 39% and AdMnSOD slowed tumor growth by 35%. AdGPx also decreased plating efficiency and growth in soft agar. The combination of AdGPx and AdMnSOD had the greatest effect on tumor cell growth suppression with a 71% reduction in cell growth compared to controls. In vivo, either AdGPx or AdMnSOD alone slowed tumor growth by 51% and 54%, respectively, while the combination of AdGPx and AdMnSOD potentiated tumor growth suppression by 81% of controls and increased animal survival. GPx may be a tumor suppressor gene in pancreatic cancer. Delivery of the GPx gene alone or in combination with the MnSOD gene may prove beneficial for treatment of pancreatic cancer.