This study examines the influence of IL‐7 on post‐thymic CD4⁺ T cells using cord blood as a model system. Survival of naive cord blood T cells in the presence of IL‐7 alone was significantly prolonged by up‐regulating bcl‐2, thereby preventing apoptosis while maintaining maximal cell viability. Cultures without IL‐7 showed high rates of apoptosis resulting in 50 % cell death by day 5 of culture. Upon phorbol 12‐myristate 13‐acetate + ionomycin stimulation, accumulation of cytoplasmic IL‐2 was similar to that observed in freshly isolated cells, but no IL‐4‐ or IFN‐γ‐positive cells were detected. IL‐7 maintained the naive T cells in a quiescent state expressing the CD45RA antigen. A significant finding was the loss of CD38 antigen expression on the naive cord blood T cells to levels similar to that observed on adult naive T cells. In contrast to the reduced proliferative response of fresh cord blood T cells to anti‐CD2 + CD28 stimulation, the proliferative response of IL‐7‐treated cells was similar to that of adult naive T cells. This study shows that as well as maintaining the naive T cell pool by enhancing cell survival and up‐regulating bcl‐2 expression, IL‐7 also functions as a maturation factor for post‐thymic naive T cells.