Patients infected with human immunodeficiency virus (HIV) frequently have increased production of interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-alpha), and these cytokines may in turn contribute to the disease pathogenesis. It has been hypothesized that secretion of these cytokines by HIV-exposed mononuclear cells or HIV-infected monocyte/macrophages (M/Ms) is the principal source of their overproduction in HIV-infected patients, and the present study was undertaken to explore this issue. We observed that in the absence of endotoxin or cytokines, M/Ms productively infected by HIV do not produce detectable IL-6 or TNF-alpha. However, granulocyte-macrophage colony-stimulating factor (GM-CSF), a cytokine that enhances HIV replication in M/Ms and is frequently used to propagate monocytotropic strains of HIV, can induce the relatively long-term production of IL-6 (up to 47 U/ml) and TNF-alpha (up to 47 pg/ml) by M/Ms, even in the absence of HIV. Also, HIV induced production of a relatively small (< or = 9 U/ml) quantity of IL-6 in M/Ms stimulated with macrophage-colony stimulating factor (M-CSF). Finally, while highly concentrated HIV induced production of both cytokines by either M/Ms or peripheral blood mononuclear cells (PBMCs), this production was almost completely eliminated when care was taken to avoid contamination of HIV by endotoxin. These data suggest that the excess IL-6 and TNF-alpha in HIV-infected patients does not simply result from their production by HIV-infected M/Ms and that alternative mechanisms are involved in this process.