The role of gap junctional intercellular communication during inflammatory processes is not well understood. In particular, changes in the expression and function of vascular endothelial connexins (gap junction proteins) in response to inflammatory agents has not been fully investigated. In this study, we used intercellular dye transfer methods to assess interendothelial communication in aortic segments isolated from mice treated with or without intraperitoneal lipopolysaccharide (LPS), a potent inflammatory mediator. LPS treatment resulted in a 49% decrease in endothelial dye coupling 18 h after injection. Western blots indicated that LPS treatment also caused a reduction in endothelial connexin40 (Cx40) levels to 33% of control levels. Connexin37 (Cx37) levels decreased only slightly after LPS treatment to 79% of control levels. We also examined endothelial communication in aortic segments isolated from Cx37–/–and Cx40–/–mice. LPS treatment caused a significantly greater decrease in dye transfer in endothelium isolated from Cx37–/–animals compared with endothelium from Cx40–/–animals (71 vs. 26% decrease). LPS injection caused a reduction in Cx40 levels in Cx37–/–endothelium, whereas LPS actually increased Cx37 levels in Cx40–/–endothelium. These results suggest that LPS mediates changes in endothelial gap junction-mediated communication, at least in part, through modulation of Cx40 and Cx37 levels.