The in vitro growth of both circulating granulocyte-macrophage (CFU-GM) and erythroid (BFU-E) progenitor cells was assessed in 29 individuals infected with the human immunodeficiency virus (HIV) at different stages of infection. The effects of autologous T lymphocytes, adherent cells, and serum on the in vitro growth of hematopoietic progenitor cells were also investigated. Compared with normal controls, baseline growth was significantly reduced for both CFU-GM and BFU-E in HIV-infected patients, independent of the clinical stage of the disease. In HIV-infected subjects depletion of autologous T cells was associated with a significant increase of progenitor cell growth. Similar results were observed after selective depletion of CD8+ T cells, while readdition of T cells to T-depleted mononuclear cells reduced the number of CFU-GM. A dose-dependent colony inhibitory activity was found in conditioned medium of T cells from HIV-infected subjects. Neither autologous adherent cells nor serum from either HIV+ or HIV- subjects had any significant effect on the in vitro growth of CFU-GM. These results indicate that the in vitro growth of circulating hematopoietic progenitor cells is impaired even in the early stages of HIV infection, and that autologous T cells exert an inhibitory effect on the in vitro growth of progenitor cells, possibly via soluble mediator(s).