Elevated levels of circulating tumor necrosis factor (TNF)-α and interleukin (IL)-6 have been detected in human immunodeficiency virus (HIV) type 1 infection. The overproduction of these cytokines could contribute to AIDS pathogenesis. Thus, the expression of TNF-α and IL-6 in human macrophages infected with HIV-1 was investigated. HIV-1 infection, per se, did not induce any TNF-α or IL-6 production or cytokine-specific mRNA expression. In contrast, HIV-1 primed macrophages to a prolonged TNF-α and IL-6 response to lipopolysaccharide (LPS) stimulation with respect to uninfected cells. Time-course analysis and flow cytometry demonstrated that cytokine production stopped at 6 h in uninfected macrophages but continued up to 24 h in HIV-1-infected cells. RNA studies suggested that HIV-1 interfered with late steps of cytokine synthesis. No modulation of membrane CD14 was found to account for the enhanced response to LPS. Finally, the effect of HIV-1 on cytokine response could not be abolished by the antiviral compound U75875.