T-cell population consists of two major subsets, CD4 T cells and CD8 T cells, which can be distinguished by the expression of CD4 or CD8 molecules, respectively. Although they play quite different roles in the immune system, many of their basic cellular processes such as proliferation following stimulation are presumably common. In this study, we have carefully analyzed time-course of G0/1 transition as well as cell cycle progression in the two subsets of quiescent T-cell population following in vitro growth stimulation. We found that CD8 T cells promote G0/1 transition more rapidly and drive their cell cycle progression faster compared to CD4 T cells. In addition, expression of CD25 and effects of its blockade revealed that IL-2 is implicated in the rapid progression, but not the earlier G0/1 transition, of CD8 T cells.