In vitro, HIV-1 infection of human fetal glial cells initiates a noncytopathic, productive infection that results in a long-term persistence during which the viral genome remains latent. The cytokines tumor necrosis factor alpha (TNF-alpha) and interleukin 1 beta (IL-1 beta) reactivate HIV-1 gene expression in these cells, leading to production of infectious virus. Here we show that treatment of human fetal glial cells with TNF-alpha and IL-1 beta increase expression of the reporter gene chloramphenicol acetyltransferase (CAT) when placed under the control of the HIV-1 5' LTR. We also show that treatment of human fetal glial cells with TNF-alpha leads to increased binding of the nuclear transcription factor NF-kappa B (p50/p65) to a consensus kappa B-binding site present in the HIV-1 5'LTR. Our results suggest that TNF-alpha stimulation of HIV-1 gene expression in primary cultures of human fetal glial cells is mediated by an increase in binding of NF-kappa B (p50/p65) to the HIV-1 LTR. This is the first report documenting NF-kappa B-binding activity in primary cultures of human fetal glial cells.