The accumulation of leukocytes in the vasculature at inflammatory sites and their migration into the local tissue is a multistep process, which is mediated by various cell adhesion molecules. Among these, selectins, a family of three Ca++-dependent carbohydrate-binding proteins, initiate leukocyte tethering and rolling along the vessel wall in the vascular shear flow. Actually, their central role in the immune defence make selectins attractive targets for a new antiinflammatory therapy. The low affine selectine-ligand bonds with their rapid assoziation and dissoziation properties should mediate the rolling interaction. Furthermore, a multivalent binding of several local concentrated ligands and receptors have been hypothesized to be essential for leukocyte binding. Nevertheless, the dynamics of cell rolling and the molecular mechanisms of selectin binding their complex oligosaccharid ligands have not been fully elucidated. We therefore introduced a dynamic model system to investigate the molecular mechanisms of selectin bindings. Inside a flow-chamber, support-fixed membranes at glass slides with a defined lateral distribution of carbohydrate ligands were used as model for the vascular surface. Their interactions with selectin-containing cells in a shear rate of a flow chamber were analyzed with a confocal laser scanning microscope. Using various glycolipid ligands bearing the binding epitope Sialyl Lewisx we could show that one class of selectins alone is able to mediate cell rolling without other cell adhesion molecules. Contrary to the natural glycoprotein ligands we performed binding studies with glycolipids. Therefore we conclude that the epitope Sialyl Lewisx is able to mediate cell rolling. The fraction of rolling cells and their rolling velocity can sensitively balanced by the ligand concentration in the membrane and by the shear force. A lateral concentration (clustering) of ligands in the membrane could be illustrated as a prerequesite for rolling interactions, thus supporting the hypothesis of multivalency of binding. Additionally, the system is suitable to check the inhibitory potency of soluble compounds. Due to dynamic conditions in the flow chamber the cell binding interactions are detected under physiological conditions of rolling leukocytes. Therefore our results are discusssed more reliable than in static cell-binding-assays.