Acute ethanol exposure has the capacity to modulate immune functions, particularly, to down regulate monocyte production of inflammatory cytokines. However, the intracellular mechanisms for these effects of ethanol are yet to be understood. Considering that nuclear regulatory factor-kappa beta (NF-kappa B)/Rel is a common regulatory element of the promoter region of the inflammatory cytokine genes, herein, we tested the hypothesis that acute ethanol affects NF-kappa B activation in human monocytes. Adherence-isolated monocytes showed constitutive DNA binding activity of NF-kappa B. A clinically relevant dose (25 mM) of acute ethanol treatment in vitro increased NF-kappa B binding activity in monocytes with a preferential induction of the inhibitory, p50/p50, NF-kappa B/Rel homodimer, and resulted in no induction of the p65/p50 heterodimer. In contrast, lipopolysaccharide stimulation primarily induced the p65/p50 heterodimer that has been shown to result in gene activation. Thus, such unique activation of the inhibitory p50/p50 homodimer by acute ethanol treatment may result in inhibition rather than activation of NF-kappa B-regulated inflammatory cytokine genes. Consequently, these results suggest that physiologically relevant concentrations of ethanol may affect production of inflammatory cytokines, such as tumor necrosis factor-alpha, interleukin-1 beta, and interleukin-6 by disrupting NF-kappa B signaling in monocytes.