The study investigates the role of IL-7 in the homeostatic proliferation and survival of naïve T cells. Using an *in vitro* system, the authors demonstrate that IL-4, IL-7, and IL-15 enhance homeostatic proliferation of naïve T cells, but only IL-7 is critical for this process. Naïve T cells fail to proliferate significantly in the absence of IL-7, and their survival is also dependent on IL-7. In *in vivo* experiments, naïve T cells disappear gradually over a 1-month period when transferred into IL-7-deficient hosts. These findings suggest that IL-7 plays a crucial role in maintaining the homeostasis of naïve T cells by promoting their proliferation and survival. The study also highlights the importance of IL-7 in the regulation of T cell homeostasis, both in terms of proliferation and survival, and suggests that the overproduction of T cells in IL-7 transgenic mice may be due to the action of IL-7 on mature T cells.The study investigates the role of IL-7 in the homeostatic proliferation and survival of naïve T cells. Using an *in vitro* system, the authors demonstrate that IL-4, IL-7, and IL-15 enhance homeostatic proliferation of naïve T cells, but only IL-7 is critical for this process. Naïve T cells fail to proliferate significantly in the absence of IL-7, and their survival is also dependent on IL-7. In *in vivo* experiments, naïve T cells disappear gradually over a 1-month period when transferred into IL-7-deficient hosts. These findings suggest that IL-7 plays a crucial role in maintaining the homeostasis of naïve T cells by promoting their proliferation and survival. The study also highlights the importance of IL-7 in the regulation of T cell homeostasis, both in terms of proliferation and survival, and suggests that the overproduction of T cells in IL-7 transgenic mice may be due to the action of IL-7 on mature T cells.