This article demonstrates that human immunodeficiency virus type 1 (HIV-1) gp120 amplifies the activity of tumor necrosis factor alpha (TNF-alpha), a cytokine that stimulates HIV-1 replication through activation of NF-kappa B. In CD4-positive Jurkat cells, gp120 potentiates TNF-induced NF-kappa B activation. TNF-mediated activation of NF-kappa B is known to involve the intracellular formation of reactive oxygen intermediates (ROIs). Accordingly, we examined the influence of gp120 on the cellular redox state. We found that gp 120-modulated TNF-induced NK-kappa B activation was inhibited by the antioxidant butylated hydroxyanisole, indicating the involvement of redox-dependent mechanisms. In addition, we showed that gp120 induces intracellular formation of hydrogen peroxide, which is accompanied by a decrease in the ratio of glutathione to glutathione disulfide. In contrast, in the p56lck-deficient J.CaM1.6 T cell line, a derivative of the Jurkat cell line, gp120 was unable to stimulate hydrogen peroxide, to decrease the ratio of GSH to GSSG, and has no effect on TNF-induced NF-kappa B activation. This demonstrated that p56lck protein tyrosine kinase plays an active role in transmitting a signal that increases the oxidative state of the cell and as a consequence amplifies TNF-mediated NF-kappa B DNA binding. We have demonstrated that Tat protein decreased both the Mn-dependent superoxide dismutase (MnSOD) and the cellular glutathione content (GSH). Here we show that, in contrast to Tat, gp120 is unable to inhibit activity and expression of MnSOD and to decrease GSH content. Taken together, our data suggest that gp120 potentiates TNF-induced NF-kappa B activation by stimulating a signal pathway that involves p56lck and the increased formation of reactive oxygen intermediates such as H2O2. These findings may be relevant for the regulation of HIV-1 replication in T cells.