Manganese superoxide dismutase (MnSOD) protects cells against oxidative stress by eliminating superoxides. Hypothetically, decreased MnSOD levels in cancer might lead to increased oxidative stress and, thus, to increased sensitivity of cells to chemotherapy agents. Eighty-nine patients with acute myeloid leukemia (AML) were analyzed for a functional C to T polymorphism of MnSOD, which could potentially lead to decreased enzyme concentrations inside mitochondria. A significant survival advantage (p=0.02) was observed for those AML patients carrying T-containing alleles of MnSOD compared to the patients with the CC genotype. These preliminary results may indicate an important role for genetic factors regulating the cellular redox state in determining the outcome of leukemia chemotherapy.