Integrins are a family of dimeric proteins that mediate cell-to-cell and extracellular matrix adhesion. They consist of a large α chain that is non-covalently associated with a smaller β chain which defines the integrin subfamilies. VLA-3 (Very Late Antigen-3), a member of the integrin superfamily, exhibits elevated expression on B lymphocytes, but is also found on monocytes, platelets, and hematopoietic progenitor cells. A heterodimer of α3 (CD49c) and β1 (CD29) subunits, VLA is a receptor for laminin, fibronectin, and collagen. The α3 chain contains a large extracellular domain with three putative metal-binding sequences, a transmembrane domain, and a short cytoplasmic tail. Differing requirements for divalent cations and the influence of RGD peptides results in multiple ligand-binding mechanisms for VLA-3. Although its expression is restricted in normal tissues, VLA-3 is found on a variety of cultured tumor cells. In addition, levels of VLA-3 have been shown to correlate with the degree of invasiveness of malignant melanoma cells. Thus, VLA-3 mediates intercellular adhesion and cell migration in normal and, possibly, cancerous cell types.