The adhesion of leukocytes to vascular endothelium is crucial for the generation of inflammatory responses. The selectins and β₂-integrin (Mac-1) play a major role in the process. Recently, it was reported that RO-heparin can inhibit selectin-mediated leukocyte adhesion. The effect of RO-heparin on the Mac-1-mediated neutrophils adhesion were further tested. The results showed that RO-heparin could effectively inhibit neutrophils binding to ICAM-1, adhering to COS-7 cells expressing human ICAM-1, and adhering to human umbilical vein endothelial cells (HUVECs) under static and flow conditions. The findings suggest that the effect of RO-heparin on leukocyte adhesion is mainly due to its inhibition on the interaction between selectins or Mac-1 and their ligands and that RO-heparin might be useful in preventing inflammation diseases.