Cytokines released by mucosal monocytes play an important role in pathogenesis of inflammatory bowel disease (IBD). Among the best characterised of these cytokines is IL-8, a potent neutrophil attractant. As normal products of bacterial metabolism, secondary bile acids are present in the colonic lumen where they are known to have many roles in regulating mucosal barrier function. Here, we investigated potential roles for the naturally-occurring colonic bile acids, dexoycholic acid (DCA) and ursodeoxycholic acid (UDCA), in regulating IL-8 release from monocytes. IL-8 release from U937 monocytes was induced with either lipopolysaccharide (LPS) [1 µg/mL] or the proinflammatory cytokine, TNFα [5 ng/mL] for 24 hrs, in the absence or presence of UDCA or DCA. Supernatants were analysed for IL-8 by ELISA. IL-8 mRNA was assessed by qPCR. Levels of phospho-p38 MAPK and phospho-p65 were measured by western blotting. Statistical analysis was performed by one way ANOVA with the Newman Keul’s post-test. Treatment of U937 monocytes with TNFα or LPS induced 9.8 ± 1.2 and 7.9 ± 1.6 fold increases in IL-8 release, respectively (n = 5 – 7; p < 0.001). At physiologically-relevant levels, DCA [25 µM] reduced both TNFα and LPS-driven IL-8 release to 4.6 ± 0.4 and 4.2 ± 0.6 fold of controls, respectively (n = 5 – 7; p < 0.05). In contrast, UDCA [100 µM] reduced TNFα-, but not LPS-driven, IL-8 release to 3.5 ± 0.4 fold of controls (n = 5; p < 0.001). UDCA also inhibited IL-8 mRNA expression (n = 4; p < 0.05). The cell surface bile acid receptor, TGR5, was found to be expressed in monocytes, while the nuclear receptor, FXR, was not. However, activation of TGR-5 with a specific agonist, INT777 (1 – 100 µM), did not alter IL-8 release. The NFkB inhibitor, BMS-345541 (10 µM), attenuated both TNFα and LPS-induced IL-8 release (n = 4; p < 0.05). While DCA had no effect, UDCA specifically reduced TNFα-, but not LPS-, induced NFkB activation. Both TNFα and LPS stimulated phosphorylation of p38 MAPK, while a p38 MAPK inhibitor, SB203580 (10 µM), attenuated LPS, but not TNFα-induced IL-8 secretion. Interestingly, UDCA did not alter TNFα- or LPS-induced p38 MAPK activation, while DCA potentiated p38 activation in response to both stimuli (n = 4 – 6; p < 0.05). These studies underline the importance of bile acids in regulating intestinal physiology and demonstrate a strict structural specificity of their actions. Attenuation of cytokine release from monocytes by DCA at physiologically-relevant concentrations may serve to dampen intestinal inflammation under normal circumstances, while the more specific effects of UDCA at relatively high concentrations may be important under therapeutic conditions. In summary, by virtue of their anti-inflammatory effects on monocytes, bile acids represent good targets for development of new approaches to treat IBD.