The phenotype and function of splenic DC populations from diabetes-prone NOD mice were chara-cterized and compared to DC from diabetes-resistant strains in the presence or absence of Flt3 ligand (FL) treatment. NOD mice were found to have significantly fewer CD8α⁺ DC than both B10.BR and C57BL/6 mice, and this defect was reversed by FL treatment. Freshly isolated CD8α⁺ and CD8α^– DC from all three strains were found to express similar levels of costimulatory molecules and this was similar in both FL-treated and untreated animals. IL-12 p40 production was significantly lower in purified CD11c⁺ DC from NOD mice compared to DC from C57BL/6 or B10.BR mice. CD8α⁺ DC isolated from NOD mice produced lower levels of IL-12p40 than CD8α⁺ DC from C57CBL/6 and this was dependent on the nature of the stimulus given. In contrast both CD8α⁺ and CD8α^– DC from FL-treated mice produced high levels of IL-12p40 following activation, but only the CD8α^– DC produced IL-12p70. Functionally, freshly isolated CD8α^– DC were more stimulatory than CD8α⁺ DC in a primary allogeneic mixed lymphocyte reaction. However, DC maturation resulted in increased T cell stimulatory capacity for both DC subsets, and this pattern was seen in all strains. These results demonstrate significant differences in phenotype and function of splenic NOD CD8α⁺ DC, and further suggest that FL treatment may reverse some of these abnormalities.