L eukocyte 12-lipoxygenase (12-LO) gene expression in pancreatic β cells is upregulated by cytotoxic cytokines like IL-1β. Recent studies have demonstrated that 12-LO inhibitors can prevent glutamate-induced neuronal cell death when intracellular glutathione stores are depleted. Therefore, 12-LO pathway inhibition may prevent β-cell cytotoxicity. To evaluate the role of 12-LO gene expression in immune-mediated islet destruction, we used 12-LO knockout (12-LO KO) mice. Male homozygous 12-LO KO mice and control C57BL/6 mice received 5 consecutive daily injections of low-dose streptozotocin to induce immune-mediated diabetes. Fasting serum glucose and insulin levels were measured at 7-day intervals, and the mice were followed up for 28 days. 12-LO KO mice were highly resistant to diabetes development compared with control mice and had higher serum insulin levels on day 28. Isolated pancreatic islets were treated with IL-1β, TNF-α, and IFN-γ for 18 hours. Glucose-stimulated insulin secretion in cytokine-treated islets from C57/BL6 mice decreased 54% from that of untreated islets. In marked contrast, the same cytokine mix led to only a 26% decrease in islets from 12-LO KO mice. Furthermore, cytokine-induced 12-hydroxyeicosatetraenoic acid (12-HETE) production was absent in 12-LO KO islets but present in C57/BL6 islets. Isolated peritoneal macrophages were stimulated for 48 hours with IFN-γ + LPS and compared for nitrate/nitrite generation. 12-LO KO macrophages generated 50% less nitrate/nitrite when compared with C57BL/6 macrophages. In summary, elimination of leukocyte 12-LO in mice ameliorates low dose streptozotocin–induced diabetes by increasing islet resistance to cytokines and decreasing macrophage production of nitric oxide.