Several extrathymic T cell progenitors have been described but their various contributions to the T cell lineage puzzle are unclear. In this study, we provide evidence for a splenic Lin− Thy1. 2+ T cell-committed population, rare in B6 mice, abundant in TCRα−/−, CD3ε−/−, and nude mice, and absent in IL-7-and Rag-2-deficient mice. Neither B nor myeloid cells are generated in vivo and in vitro. The incidence of these pre-T cells is under the control of thymus and/or mature T cells, as revealed by graft experiments. Indeed, IL-7 consumption by mature T cells inhibits the growth of these pre-T cells. Moreover, the nude spleen contains an additional Lin− Thy1. 2+ CD25+ subset which is detected in B6 mice only after thymectomy. We establish that the full pre-T cell potential and proliferation capacity are only present in the c-kit low fraction of progenitors. We also show that most CCR9+ progenitors are retained in the spleen of nude mice, but present in the blood of B6 mice. Thus, our data describe a new T cell lineage restricted subset that accumulates in the spleen before migration to the thymus.