Nuclear factor kappa B (NF-kappa B) is a transcription factor that is critical for the inducible expression of multiple cellular and viral genes. DNA binding activity is essential for its function. Here, we report that gold compounds, especially aurothioglucose (AuTG), have a strong inhibitory effect on NF-kappa B-DNA binding. Our finding also reveals that Zn2+ is a necessary component of NF-kappa B for its DNA binding activity and that gold ion can efficiently block NF-kappa B-DNA binding, presumably through oxidation of the cysteins associated with zinc. This redox mechanism may provide an explanation for the observed efficacy of gold compounds in the treatment of rheumatoid arthritis.