Alloxan (AL), a potent generator of superoxide and hydroxyl radicals, selectively destroys rodent pancreatic beta-cells. Alloxan-susceptible (ALS/Lt) and AL-resistant (ALR/Lt) are inbred mouse strains derived in Japan by inbreeding CD-1 (ICR) mice with concomitant selection for high or low sensitivity to a relatively low AL dose. The present study was undertaken to examine whether resistance was mediated by differences in either systemic or beta-cell antioxidant defense status. Superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), and glutathione peroxidase (GPX) activities were determined in tissues of AL-untreated ALR/Lt and ALS/Lt male mice at 7 weeks of age. Specific activities of pancreatic SOD1, GR, and GPX were significantly increased in ALR/Lt mice compared with ALS/Lt mice. ALR/Lt mice further exhibited higher levels of glutathione in plasma, blood, pancreas, and liver combined with lower constitutive lipid peroxides in serum, liver, and pancreas. These results support the hypothesis that the selection process leading to the development of an AL-resistant mouse strain entailed accumulation of a gene or genes contributing to upregulated antioxidant status.