Pyrrolidine dithiocarbamate (PDTC) is a metal-chelating compound that acts as antioxidant or pro-oxidant and is widely used to study redox regulation of cell function. In the present study, we investigated effects of PDTC and another antioxidant, N-acetyl-l -cysteine (NAC), on TNF-α-dependent activation of NF-κB in human aortic smooth muscle cells (HASMC). Treatment of the cells with TNF-α induced the activation of p65/p50 heterodimer NF-κB and increased the mRNA levels of monocyte chemoattractant protein (MCP)-1. Pretreatment with PDTC markedly suppressed the NF-κB activation and expression of MCP-1 by inhibiting IκB-α degradation. In contrast, NAC had no effect. PDTC concomitantly increased the intracellular levels of copper, and bathocuproinedisulfonic acid, a non-cell-permeable chelator of Cu¹⁺, inhibited the PDTC-induced increase in intracellular copper level and reversed the PDTC effects on IκB-α, NF-κB, and MCP-1. These results indicate that TNF-α-dependent expression of MCP-1 in HASMC is tightly regulated by NF-κB and that intracellular copper level is crucial for the TNF-α-dependent activation of NF-κB in HASMC.