Interleukin (IL)-7 enhances CD8 T-cell proliferation and cytolytic activity. The expression of its receptor, CD127 (IL-7R alpha), may therefore be important in the immunopathogenesis of HIV disease. CD127 expression on CD8(+) T cells from HIV seronegative controls, untreated HIV-seropositive patients, and HIV-positive patients receiving antiretroviral therapy with sustained viral suppression was analyzed by flow cytometry in a cross-sectional study. Among healthy controls, 65% of CD8 cells expressed CD127 ( n = 7). This dropped to 21.6% among untreated HIV-positive patients ( n = 16), and approached normal levels (47.7%) in HIV-positive individuals on effective therapy ( n = 20). The same pattern was observed for naïve (CD45RA(+) ) and memory (CD45RO(+) ) CD8(+) T cells but changes were more extreme within the memory cell population. Duration of viral suppression was the only parameter evaluated that correlated with extent of CD127 expression in treated patients. Impairment of CTL activity in HIV disease may be caused, in part, by downregulation of IL-7 receptor expression. Improved immune function with effective antiretroviral therapy is associated with recovery of this molecule. The correlation between virologic suppression and apparent CD127 recovery suggests that essential cytokine signaling pathways may be restored with sustained inhibition of viral replication.