Pharmacological inhibition of interleukin-12 (IL-12) production may allow a therapeutic strategy for preventing development and progression of disease in experimental models of autoimmunity. In this study we investigated the effects of an ethanol fraction .of the Scapharca broughtonii, on the production of IL-12 by mouse macrophages stimulated with lipopolysaccharides (LPS). The ethanol fraction (S3) prepared from Scapharca broughtonii potently Inhibited LPS-induced IL-12 production in the RAW264.7 monocyte cell-line in a dose-dependent manner. The activation effect of the ethanol fraction (S3) on the IL-12 gene promoter was analyzed by transfecting RAW264.7 cell with IL-12 gene promoter that contained a binding site for NFkB. Furthermore, activation of macrophages by LPS resulted in markedly enhanced binding activity to the NF-kB site, which significantly decreased upon addition of the ethanol fraction, indication that the ethanol fraction of the blood shell inhibited IL-12 production in LPS-activated macrophages via inhibition of NF-kB binding activity.