In mouse models, CD4+CD25+ T cells are involved in maintenance of peripheral tolerance. In humans, a subset of CD4+CD25+ T cells expressing high levels of CD25 (CD4+CD25high) with characteristics identical to murine CD4+CD25+ was recently described. We evaluated the characteristics of CD4+CD25high T cells in peripheral blood of type 1 diabetic subjects (T1D) and normal controls (NC). In contrast to a previous report, we found no difference in the number of CD4+CD25high and CD4+CD25+ T cells between T1D and NC. We confirmed previous studies that demonstrated that human CD4+CD25high cells can suppress the proliferation of co-cultured CD4+CD25- cells stimulated in conditions of sub-maximal cross-linking by anti-CD3 either with or without anti-CD28. However, we did not observe statistical differences between the normal controls and the chronic diabetic subjects we tested. Culturing of these cell populations did not appear to affect their ability to suppress proliferation in both groups. In conclusion, we found no significant differences in number or in vitro regulatory function of CD4+CD25high in chronic human T1D subjects.