Human immunodeficiency virus (HIV) production from latently infected T lymphocytes can be induced with compounds that activate the cells to secrete lymphokines. The elements in the HIV genome which control activation are not known but expression might be regulated through a variety of DNA elements. The cis-acting control elements of the viral genome are enhancer and promoter regions. The virus also encodes trans-acting factors specified by the tat-III and art genes. We have examined whether products specific to activated T cells might stimulate viral transcription by binding to regions on viral DNA. Activation of T cells, which increases HIV expression up to 50-fold, correlated with induction of a DNA binding protein indistinguishable from a recognized transcription factor, called NF-kappa B, with binding sites in the viral enhancer. Mutation of these binding sites abolished inducibility. That NF-kappa B acts in synergy with the viral tat-III gene product to enhance HIV expression in T cells may have implications for the pathogenesis of AIDS (acquired immune deficiency syndrome).