Mononuclear cells play an important role in the regulation of microbe-induced inflammation, in part through their ability to secrete cytokines in response to microorganisms and their products. To evaluate the effects of Desulfovibrio desulfuricans-derived endotoxins on TNF-α induction, lipopolysaccharides (LPSs) isolated from soil and intestinal strain were used to stimulate peripheral blood mononuclear cells. The effect of these LPSs was assessed in comparison to that of LPSs from Escherichia coli, Salmonella minnesota and of lipid A from Salmonella minnesota. Level of TNF-α was measured by enzyme-linked immunosorbent assay. D. desulfuricans LPSs at the highest dose (1000 ng/ml) displayed greater biological potency in inducing TBF-α secretion than other endotoxins used which indicates that these LPSs may act as a criticalvregulatory factor in bacteremia caused by these microorganisms.