Impaired haematopoiesis during HIV-1 infection may be caused by the overproduction of inflammatory cytokines by immune cells at the bone marrow level inducing Fas-mediated apoptosis of stem progenitors. In this study, we evaluated the effects of highly active antiretroviral therapy on apoptosis of CD34+ stem cells derived from the bone marrow of HIV-1-infected patients, and observed decreased Fas expression on progenitor cells, in parallel with the diminution of TNF-alpha levels and the amelioration of clonogenic parameters.