Cluster of differentiation 68 (CD68) is a heavily glycosylated transmembrane antigen that is detected in lysosomes, tissue macrophages, Langerhans cells, dendritic cells, monocytes, Kupffer cells, osteoclasts, and granulocytes. The CD68 antigen is involved in phagocytic activities of tissue macrophages, both in intracellular lysosomal metabolism and extracellular cell-cell and cell-pathogen interactions. CD68 binds to tissue- and organ-specific lectins and selectins, allowing homing of macrophage subsets to particular sites. Rapid recirculation of CD68 from endosomes and lysosomes to the plasma membrane helps macrophages to move over selectin-bearing substrates and other cells. CD68 is highly expressed by blood monocytes and tissue macrophages as well as many tumor cell lines promoting binding to selectins on vascular endothelium facilitating dissemination to secondary sites.