Interendothelial junctions in continuous endothelium are the primary pathway for the passage of fluid, solutes, and leukocytes from the intravascular compartment to the interstitium. The maintenance of these channels is in part a function of circulating metabolites and local secretions produced by the cells of the microvessel wall. When this regulatory mechanism is disrupted, such as in an acute inflammatory response, interendothelial gaps appear and the microvascular barrier is compromised. Glycosylated cell surface proteins are believed to play a role in the development and maintenance of junctional apposition, and hence permeability. A predictable response of microvascular endothelial cells to an inflammatory stimulus therefore should be a change in junction-associated glycoproteins. Moreover, the heterogeneity of microvascular endothelial barrier properties may in part be a function of specific glycans involved in cell-cell contact. To test these suppositions, the binding of a panel of lectins to cultured endothelial and mesothelial cells is observed and compared under resting and stimulated (with the inflammatory agonist thromboxane) conditions. The binding of wheat germ agglutinin to cell borders is greater than for other lectins tested in both endothelial and mesothelial cell cultures. After confluence, binding sites at the junction disappear in endothelial cells but remain in mesothelial cells. A thromboxane-mimic (CTA2) induces gap formation, a redistribution of wheat germ agglutinin binding sites and an increase in intercellular permeability. These changes correlate with our published studies on the time and extent of endothelial contractions and corresponding increased permeability of an EC monolayer induced by thromboxane and other inflammatory agents.