The NOD (nonobese diabetic) mouse strain develops a characteristic autoimmune syndrome that closely resembles human type I diabetes. It has been suggested that NOD mice exhibit both numerical deficiency in CD4+CD25+ regulatory T cells (Treg) and reduced suppressive activity. We compared sorted CD4+CD25+ Tregs from the spleens of 6-7 week-old female NOD and nondiabetic B6.H2g7 mice. Tregs were 93±2% and 95±1% Foxp3+ in NOD and B6.H2g7 cells, respectively, on post-sort reanalysis. "Conventional" CD4+CD25- T cells (Tconv) are included as reference populations. Surprisingly, Treg "signature" is similar between the two strains, with only a few probesets that subtly deviate. Keywords: Cell population comparison from two mouse strains. Overall design: For each strain (NOD and B6.g7), we analyzed two populations: CD4+CD25+ Treg and CD4+CD25- Tconv cells, for a total of four distinct populations. RNA from three mice were pooled for each replicate; there are three independent replicates for each population. After RMA normalization, intensity values were averaged across the three replicates and analyzed. We calculated the ratio of Treg/Tconv intensity values for each strain and compared the results.